/* ============================================================
   Periodic Table of Elements - Main Stylesheet
   periodictableofelements.org
   ============================================================ */

/* --- Theme Variables (Dark Mode Default) --- */
:root {
    --bg-primary: #0a0e17;
    --bg-secondary: #111827;
    --bg-card: #1a1f2e;
    --bg-card-hover: #252b3d;
    --text-primary: #e8edf5;
    --text-secondary: #8892a4;
    --text-muted: #5a6478;
    --border-color: #2a3042;
    --accent: #6c9fff;
    --accent-hover: #8bb4ff;
    --accent-glow: rgba(108, 159, 255, 0.25);
    --tooltip-bg: #1e2538;
    --controls-bg: rgba(17, 24, 39, 0.9);
    --input-bg: #1a2035;
    --input-border: #2a3555;
    --legend-bg: rgba(17, 24, 39, 0.85);
    --shadow: 0 4px 24px rgba(0, 0, 0, 0.3);
    --success: #22c55e;
    --success-bg: rgba(34, 197, 94, 0.12);
    --success-border: rgba(34, 197, 94, 0.3);
    --danger: #f87171;
    --danger-bg: rgba(248, 113, 113, 0.12);
    --danger-border: rgba(248, 113, 113, 0.3);
    --warning: #fbbf24;
    --warning-bg: rgba(251, 191, 36, 0.12);
    --warning-border: rgba(251, 191, 36, 0.3);
}

[data-theme="light"] {
    --bg-primary: #f0f4f8;
    --bg-secondary: #ffffff;
    --bg-card: #ffffff;
    --bg-card-hover: #f5f7fa;
    --text-primary: #1a202c;
    --text-secondary: #4a5568;
    --text-muted: #a0aec0;
    --border-color: #e2e8f0;
    --accent: #3b82f6;
    --accent-hover: #2563eb;
    --accent-glow: rgba(59, 130, 246, 0.2);
    --tooltip-bg: #ffffff;
    --controls-bg: rgba(255, 255, 255, 0.9);
    --input-bg: #f7fafc;
    --input-border: #e2e8f0;
    --legend-bg: rgba(255, 255, 255, 0.9);
    --shadow: 0 4px 24px rgba(0, 0, 0, 0.08);
    --success: #16a34a;
    --success-bg: rgba(22, 163, 74, 0.1);
    --success-border: rgba(22, 163, 74, 0.3);
    --danger: #dc2626;
    --danger-bg: rgba(220, 38, 38, 0.1);
    --danger-border: rgba(220, 38, 38, 0.3);
    --warning: #d97706;
    --warning-bg: rgba(217, 119, 6, 0.1);
    --warning-border: rgba(217, 119, 6, 0.3);
}


/* ============================================================
   Global Base Styles
   ============================================================ */
html {
    overflow-x: hidden;
}

body {
    background: var(--bg-primary);
    color: var(--text-primary);
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    transition: background 0.3s, color 0.3s;
    overflow-x: hidden;
}

main {
    padding: 0;
}

a {
    color: var(--accent);
    transition: color 0.2s;
}

a:hover {
    color: var(--accent-hover);
}

hr {
    border-color: var(--border-color);
    opacity: 0.5;
}

::selection {
    background: var(--accent);
    color: #fff;
}


/* ============================================================
   Navbar
   ============================================================ */
.navbar {
    background: var(--bg-secondary);
    border-bottom: 1px solid var(--border-color);
    padding: 0.5rem 0;
}

.navbar .navbar-brand {
    color: var(--text-primary);
    font-weight: 700;
    text-decoration: none;
    min-width: 0;
    overflow: hidden;
}

.navbar .navbar-brand:hover {
    color: var(--text-primary);
}

.brand-element-box {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    width: 34px;
    height: 34px;
    background: linear-gradient(135deg, var(--accent), #4f7cdb);
    color: #fff;
    font-family: 'Spectral', serif;
    font-weight: 700;
    font-size: 1rem;
    border-radius: 6px;
    letter-spacing: -0.5px;
    box-shadow: 0 0 12px var(--accent-glow);
    flex-shrink: 0;
}

.brand-text {
    font-family: 'Spectral', serif;
    font-size: 1.15rem;
    font-weight: 700;
    letter-spacing: -0.3px;
    overflow: hidden;
    text-overflow: ellipsis;
    white-space: nowrap;
    min-width: 0;
}

.navbar .nav-link {
    color: var(--text-secondary);
    font-size: 0.9rem;
    font-weight: 500;
    padding: 0.6rem 0.85rem;
    transition: color 0.2s;
}

.navbar .nav-link:hover,
.navbar .nav-link:focus {
    color: var(--accent);
}

.navbar .nav-link.active {
    color: var(--accent);
    font-weight: 600;
}

.navbar .dropdown-menu {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: 8px;
    box-shadow: var(--shadow);
    padding: 0.35rem 0;
    margin-top: 0.25rem;
}

.navbar .dropdown-item {
    color: var(--text-primary);
    font-size: 0.88rem;
    padding: 0.5rem 1rem;
    transition: background 0.15s, color 0.15s;
}

.navbar .dropdown-item:hover,
.navbar .dropdown-item:focus {
    background: var(--bg-card-hover);
    color: var(--accent);
}

.navbar .dropdown-item.active {
    background: var(--accent-glow);
    color: var(--accent);
}

.btn-outline-accent {
    color: var(--accent);
    border: 1px solid var(--accent);
    background: transparent;
    font-size: 0.88rem;
    font-weight: 500;
    padding: 0.4rem 1rem;
    border-radius: 6px;
    transition: all 0.2s;
    text-decoration: none;
    white-space: nowrap;
}

.btn-outline-accent:hover {
    background: var(--accent);
    color: #fff;
    box-shadow: 0 0 16px var(--accent-glow);
}

/* Navbar toggler icon adapts to theme */
.navbar-toggler {
    border-color: var(--border-color);
}

.navbar-toggler-icon {
    background-image: url("data:image/svg+xml,%3csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 30 30'%3e%3cpath stroke='rgba(100,116,139,1)' stroke-linecap='round' stroke-miterlimit='10' stroke-width='2' d='M4 7h22M4 15h22M4 23h22'/%3e%3c/svg%3e");
}

[data-theme="dark"] .navbar-toggler-icon {
    background-image: url("data:image/svg+xml,%3csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 30 30'%3e%3cpath stroke='rgba(160,174,192,1)' stroke-linecap='round' stroke-miterlimit='10' stroke-width='2' d='M4 7h22M4 15h22M4 23h22'/%3e%3c/svg%3e");
}

.brand-tld {
    color: var(--text-muted);
    font-weight: 400;
}


/* ============================================================
   Footer
   ============================================================ */
.site-footer {
    background: var(--bg-secondary);
    border-top: 1px solid var(--border-color);
    padding: 2.5rem 0 0;
    margin-top: auto;
}

.footer-top {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(160px, 1fr));
    gap: 2rem;
    padding-bottom: 2rem;
    border-bottom: 1px solid var(--border-color);
}

.footer-heading {
    color: var(--text-primary);
    font-size: 0.8rem;
    font-weight: 600;
    text-transform: uppercase;
    letter-spacing: 0.08em;
    margin-bottom: 0.75rem;
}

.footer-links {
    list-style: none;
    padding: 0;
    margin: 0;
}

.footer-links li {
    margin-bottom: 0.4rem;
}

.footer-links a {
    color: var(--text-secondary);
    text-decoration: none;
    font-size: 0.88rem;
    transition: color 0.2s;
}

.footer-links a:hover {
    color: var(--accent);
}

.footer-bottom {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 0.6rem;
    padding: 1.25rem 0;
    color: var(--text-muted);
    font-size: 0.82rem;
}

.footer-element-badge {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    width: 24px;
    height: 24px;
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: 4px;
    font-family: 'Spectral', serif;
    font-weight: 700;
    font-size: 0.7rem;
    color: var(--accent);
}


/* ============================================================
   Bootstrap Overrides - Dark Theme
   ============================================================ */

/* --- Buttons --- */
.btn-primary {
    background: var(--accent);
    border-color: var(--accent);
    color: #fff;
}

.btn-primary:hover,
.btn-primary:focus {
    background: var(--accent-hover);
    border-color: var(--accent-hover);
    color: #fff;
    box-shadow: 0 0 16px var(--accent-glow);
}

.btn-primary:active {
    background: var(--accent);
    border-color: var(--accent);
}

.btn-danger {
    background: #991b1b;
    border-color: #991b1b;
    color: #fecaca;
}

.btn-danger:hover,
.btn-danger:focus {
    background: #b91c1c;
    border-color: #b91c1c;
    color: #fff;
}

.btn-outline-primary {
    color: var(--accent);
    border-color: var(--accent);
}

.btn-outline-primary:hover {
    background: var(--accent);
    border-color: var(--accent);
    color: #fff;
}

.btn-secondary {
    background: var(--bg-card);
    border-color: var(--border-color);
    color: var(--text-primary);
}

.btn-secondary:hover {
    background: var(--bg-card-hover);
    border-color: var(--accent);
    color: var(--text-primary);
}

/* --- Forms --- */
.form-control {
    background: var(--input-bg);
    border: 1px solid var(--input-border);
    color: var(--text-primary);
    border-radius: 6px;
    transition: border-color 0.2s, box-shadow 0.2s;
}

.form-control:focus {
    background: var(--input-bg);
    border-color: var(--accent);
    color: var(--text-primary);
    box-shadow: 0 0 0 3px var(--accent-glow);
}

.form-control::placeholder {
    color: var(--text-muted);
}

.form-control:disabled,
.form-control[readonly] {
    background: var(--bg-card);
    color: var(--text-muted);
    opacity: 0.7;
}

.form-select {
    background-color: var(--input-bg);
    border: 1px solid var(--input-border);
    color: var(--text-primary);
    border-radius: 6px;
}

.form-select:focus {
    background-color: var(--input-bg);
    border-color: var(--accent);
    color: var(--text-primary);
    box-shadow: 0 0 0 3px var(--accent-glow);
}

.form-label {
    color: var(--text-secondary);
    font-weight: 500;
    font-size: 0.9rem;
    margin-bottom: 0.35rem;
}

.form-text {
    color: var(--text-muted);
}

.form-check-input {
    background-color: var(--input-bg);
    border-color: var(--input-border);
}

.form-check-input:checked {
    background-color: var(--accent);
    border-color: var(--accent);
}

.form-check-label {
    color: var(--text-secondary);
}

.input-group-text {
    background: var(--bg-card);
    border-color: var(--input-border);
    color: var(--text-secondary);
}

/* --- Alerts --- */
.alert-danger {
    background: var(--danger-bg);
    border: 1px solid var(--danger-border);
    color: var(--danger);
}

.alert-danger a {
    color: var(--danger);
    font-weight: 600;
}

.alert-success {
    background: var(--success-bg);
    border: 1px solid var(--success-border);
    color: var(--success);
}

.alert-success a {
    color: var(--success);
    font-weight: 600;
}

.alert-warning {
    background: var(--warning-bg);
    border: 1px solid var(--warning-border);
    color: var(--warning);
}

.alert-info {
    background: rgba(108, 159, 255, 0.1);
    border: 1px solid rgba(108, 159, 255, 0.25);
    color: var(--accent);
}

.alert ul {
    margin: 0;
    padding-left: 1rem;
}

/* --- Cards --- */
.card {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: 10px;
    color: var(--text-primary);
}

.card-header {
    background: var(--bg-secondary);
    border-bottom: 1px solid var(--border-color);
    color: var(--text-primary);
}

.card-footer {
    background: var(--bg-secondary);
    border-top: 1px solid var(--border-color);
}

.card-title {
    color: var(--text-primary);
}

.card-text {
    color: var(--text-secondary);
}

/* --- Tables --- */
.table {
    color: var(--text-primary);
    border-color: var(--border-color);
}

.table > thead {
    color: var(--text-secondary);
    border-bottom: 2px solid var(--border-color);
}

.table > thead th {
    font-weight: 600;
    font-size: 0.85rem;
    text-transform: uppercase;
    letter-spacing: 0.03em;
    color: var(--text-secondary);
}

.table > tbody > tr {
    border-color: var(--border-color);
}

.table > tbody > tr > td {
    padding: 0.65rem 0.75rem;
    vertical-align: middle;
}

.table-striped > tbody > tr:nth-of-type(odd) {
    background: rgba(255, 255, 255, 0.02);
    color: var(--text-primary);
}

.table-hover > tbody > tr:hover {
    background: var(--bg-card-hover);
    color: var(--text-primary);
}

/* --- Badges --- */
.badge {
    font-weight: 500;
    font-size: 0.78rem;
}

.badge.bg-primary,
.badge.text-bg-primary {
    background: var(--accent) !important;
    color: #fff;
}

.badge.bg-secondary,
.badge.text-bg-secondary {
    background: var(--bg-card) !important;
    color: var(--text-secondary);
    border: 1px solid var(--border-color);
}

.badge.bg-success,
.badge.text-bg-success {
    background: var(--success-bg) !important;
    color: var(--success);
    border: 1px solid var(--success-border);
}

.badge.bg-danger,
.badge.text-bg-danger {
    background: var(--danger-bg) !important;
    color: var(--danger);
    border: 1px solid var(--danger-border);
}

.badge.bg-warning,
.badge.text-bg-warning {
    background: var(--warning-bg) !important;
    color: var(--warning);
    border: 1px solid var(--warning-border);
}

/* --- Modals --- */
.modal-content {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    color: var(--text-primary);
}

.modal-header {
    border-bottom-color: var(--border-color);
}

.modal-footer {
    border-top-color: var(--border-color);
}

.btn-close {
    filter: invert(1) grayscale(100%) brightness(200%);
}

/* --- Pagination --- */
.page-link {
    background: var(--bg-card);
    border-color: var(--border-color);
    color: var(--text-secondary);
}

.page-link:hover {
    background: var(--bg-card-hover);
    border-color: var(--accent);
    color: var(--accent);
}

.page-item.active .page-link {
    background: var(--accent);
    border-color: var(--accent);
    color: #fff;
}

.page-item.disabled .page-link {
    background: var(--bg-secondary);
    border-color: var(--border-color);
    color: var(--text-muted);
}

/* --- Breadcrumb --- */
.breadcrumb {
    background: transparent;
    padding: 0;
}

.breadcrumb-item a {
    color: var(--accent);
}

.breadcrumb-item.active {
    color: var(--text-muted);
}

.breadcrumb-item + .breadcrumb-item::before {
    color: var(--text-muted);
}

/* --- List Group --- */
.list-group-item {
    background: var(--bg-card);
    border-color: var(--border-color);
    color: var(--text-primary);
}

.list-group-item:hover {
    background: var(--bg-card-hover);
}

.list-group-item.active {
    background: var(--accent);
    border-color: var(--accent);
}


/* ============================================================
   Page Layout Components
   ============================================================ */

/* Generic content wrapper with max-width and padding */
.page-content {
    max-width: 960px;
    margin: 0 auto;
    padding: 2rem 1.5rem;
}

/* Content section card for about, refund, generic info pages */
.content-section {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: 12px;
    padding: 2rem;
    margin-bottom: 1.5rem;
}

.content-section h2,
.content-section h3 {
    color: var(--text-primary);
    margin-bottom: 0.75rem;
}

.content-section h2 {
    font-size: 1.4rem;
    font-weight: 700;
    border-bottom: 1px solid var(--border-color);
    padding-bottom: 0.5rem;
    margin-bottom: 1rem;
}

.content-section h3 {
    font-size: 1.1rem;
    font-weight: 600;
}

.content-section p {
    color: var(--text-secondary);
    line-height: 1.7;
    margin-bottom: 1rem;
}

.content-section ul,
.content-section ol {
    color: var(--text-secondary);
    padding-left: 1.5rem;
    margin-bottom: 1rem;
}

.content-section li {
    margin-bottom: 0.35rem;
    line-height: 1.6;
}

.content-section a {
    color: var(--accent);
}

.content-section a:hover {
    color: var(--accent-hover);
    text-decoration: underline;
}


/* ============================================================
   Auth Card (Login, Register, Verify, Password Reset)
   ============================================================ */
.auth-card {
    max-width: 440px;
    margin: 3rem auto;
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: 12px;
    padding: 2.5rem 2rem;
    box-shadow: var(--shadow);
}

.auth-card h1,
.auth-card h2 {
    font-family: 'Spectral', serif;
    font-size: 1.6rem;
    font-weight: 700;
    color: var(--text-primary);
    text-align: center;
    margin-bottom: 0.4rem;
}

.auth-card .auth-subtitle {
    text-align: center;
    color: var(--text-secondary);
    font-size: 0.9rem;
    margin-bottom: 1.5rem;
}

.auth-card .form-group {
    margin-bottom: 1.25rem;
}

.auth-card .btn-primary {
    width: 100%;
    padding: 0.65rem;
    font-weight: 600;
    font-size: 0.95rem;
}

.auth-card .auth-footer {
    text-align: center;
    margin-top: 1.5rem;
    padding-top: 1rem;
    border-top: 1px solid var(--border-color);
    color: var(--text-secondary);
    font-size: 0.88rem;
}

.auth-card .auth-footer a {
    color: var(--accent);
    font-weight: 500;
}

.auth-card .auth-divider {
    display: flex;
    align-items: center;
    gap: 1rem;
    margin: 1.25rem 0;
    color: var(--text-muted);
    font-size: 0.82rem;
}

.auth-card .auth-divider::before,
.auth-card .auth-divider::after {
    content: '';
    flex: 1;
    height: 1px;
    background: var(--border-color);
}


/* ============================================================
   Legal Content (Terms, Privacy)
   ============================================================ */
.legal-content {
    max-width: 780px;
    margin: 0 auto;
    padding: 2.5rem 1.5rem;
}

.legal-content h1 {
    font-family: 'Spectral', serif;
    font-size: 2rem;
    font-weight: 700;
    color: var(--text-primary);
    margin-bottom: 0.5rem;
    text-align: center;
}

.legal-content .legal-date {
    text-align: center;
    color: var(--text-muted);
    font-size: 0.88rem;
    margin-bottom: 2rem;
}

.legal-content h2 {
    font-size: 1.3rem;
    font-weight: 700;
    color: var(--text-primary);
    margin-top: 2rem;
    margin-bottom: 0.75rem;
    padding-bottom: 0.4rem;
    border-bottom: 1px solid var(--border-color);
}

.legal-content h3 {
    font-size: 1.05rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-top: 1.5rem;
    margin-bottom: 0.5rem;
}

.legal-content p {
    color: var(--text-secondary);
    line-height: 1.75;
    margin-bottom: 1rem;
}

.legal-content ul,
.legal-content ol {
    color: var(--text-secondary);
    padding-left: 1.5rem;
    margin-bottom: 1rem;
}

.legal-content li {
    margin-bottom: 0.4rem;
    line-height: 1.65;
}

.legal-content a {
    color: var(--accent);
}


/* ============================================================
   Account Page
   ============================================================ */
.account-page {
    max-width: 800px;
    margin: 0 auto;
    padding: 2rem 1.5rem;
}

.account-page h1 {
    font-family: 'Spectral', serif;
    font-size: 1.8rem;
    font-weight: 700;
    margin-bottom: 1.5rem;
}

.account-page .account-card {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: 10px;
    padding: 1.5rem;
    margin-bottom: 1.25rem;
}

.account-page .account-card h3 {
    font-size: 1rem;
    font-weight: 600;
    color: var(--accent);
    margin-bottom: 1rem;
}

.account-page .account-detail {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 0.6rem 0;
    border-bottom: 1px solid var(--border-color);
    font-size: 0.92rem;
}

.account-page .account-detail:last-child {
    border-bottom: none;
}

.account-page .account-detail .label {
    color: var(--text-secondary);
}

.account-page .account-detail .value {
    color: var(--text-primary);
    font-weight: 500;
}


/* ============================================================
   Pricing Grid
   ============================================================ */
.pricing-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 1.5rem;
    max-width: 1000px;
    margin: 0 auto;
    padding: 2rem 1.5rem;
}

.pricing-card {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: 12px;
    padding: 2rem;
    text-align: center;
    transition: transform 0.2s, box-shadow 0.2s;
    position: relative;
}

.pricing-card:hover {
    transform: translateY(-4px);
    box-shadow: var(--shadow);
}

.pricing-card.featured {
    border-color: var(--accent);
    box-shadow: 0 0 24px var(--accent-glow);
}

.pricing-card.featured::before {
    content: 'Popular';
    position: absolute;
    top: -12px;
    left: 50%;
    transform: translateX(-50%);
    background: var(--accent);
    color: #fff;
    font-size: 0.72rem;
    font-weight: 600;
    padding: 0.2rem 0.8rem;
    border-radius: 20px;
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.pricing-card .plan-name {
    font-size: 1.1rem;
    font-weight: 600;
    color: var(--text-secondary);
    margin-bottom: 0.75rem;
}

.pricing-card .plan-price {
    font-family: 'Spectral', serif;
    font-size: 2.8rem;
    font-weight: 700;
    color: var(--text-primary);
    line-height: 1.1;
}

.pricing-card .plan-price span {
    font-size: 1rem;
    color: var(--text-muted);
    font-family: inherit;
}

.pricing-card .plan-period {
    font-size: 0.85rem;
    color: var(--text-muted);
    margin-bottom: 1.5rem;
}

.pricing-card .plan-features {
    list-style: none;
    padding: 0;
    margin: 0 0 1.5rem;
    text-align: left;
}

.pricing-card .plan-features li {
    padding: 0.4rem 0;
    color: var(--text-secondary);
    font-size: 0.9rem;
    border-bottom: 1px solid var(--border-color);
}

.pricing-card .plan-features li:last-child {
    border-bottom: none;
}

.pricing-card .plan-features li::before {
    content: '\2713';
    color: var(--success);
    font-weight: 700;
    margin-right: 0.5rem;
}


/* ============================================================
   Checkout Form
   ============================================================ */
.checkout-form {
    max-width: 520px;
    margin: 2rem auto;
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: 12px;
    padding: 2rem;
    box-shadow: var(--shadow);
}

.checkout-form h2 {
    font-family: 'Spectral', serif;
    font-size: 1.4rem;
    font-weight: 700;
    margin-bottom: 1.25rem;
}

.checkout-form .order-summary {
    background: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: 8px;
    padding: 1rem;
    margin-bottom: 1.5rem;
}

.checkout-form .order-summary .summary-row {
    display: flex;
    justify-content: space-between;
    padding: 0.35rem 0;
    color: var(--text-secondary);
    font-size: 0.9rem;
}

.checkout-form .order-summary .summary-total {
    border-top: 1px solid var(--border-color);
    margin-top: 0.5rem;
    padding-top: 0.5rem;
    font-weight: 700;
    color: var(--text-primary);
}

.checkout-form #card-element {
    background: var(--input-bg);
    border: 1px solid var(--input-border);
    padding: 0.75rem;
    border-radius: 6px;
    transition: border-color 0.2s;
}

.checkout-form #card-element:focus-within {
    border-color: var(--accent);
    box-shadow: 0 0 0 3px var(--accent-glow);
}


/* ============================================================
   Controls Bar (Periodic Table)
   ============================================================ */
.controls-bar {
    display: flex;
    align-items: center;
    gap: 1rem;
    padding: 0.75rem 1rem;
    background: var(--controls-bg);
    backdrop-filter: blur(12px);
    border-bottom: 1px solid var(--border-color);
    flex-wrap: wrap;
    position: sticky;
    top: 0;
    z-index: 100;
}

.controls-bar label {
    color: var(--text-secondary);
    font-size: 0.8rem;
    font-weight: 500;
    white-space: nowrap;
}

.controls-input {
    background: var(--input-bg);
    border: 1px solid var(--input-border);
    color: var(--text-primary);
    border-radius: 8px;
    padding: 0.5rem 0.75rem;
    font-size: 0.85rem;
    outline: none;
    transition: border-color 0.2s;
}

.controls-input:focus {
    border-color: var(--accent);
    box-shadow: 0 0 0 2px var(--accent-glow);
}

.controls-label {
    color: var(--text-secondary);
    font-size: 0.8rem;
    font-weight: 500;
    white-space: nowrap;
}

.filter-group {
    display: flex;
    align-items: center;
    gap: 0.4rem;
}

.temperature-control {
    display: flex;
    align-items: center;
    gap: 0.4rem;
    flex: 1;
    min-width: 200px;
    max-width: 350px;
}

.temperature-control input[type="range"] {
    flex: 1;
    accent-color: var(--accent);
}

.temp-value {
    color: var(--accent);
    font-size: 0.85rem;
    font-weight: 600;
    min-width: 52px;
    text-align: right;
}

.btn-theme-toggle {
    background: transparent;
    border: 1px solid var(--border-color);
    border-radius: 8px;
    color: var(--text-secondary);
    padding: 0.4rem 0.6rem;
    cursor: pointer;
    font-size: 1rem;
    transition: all 0.2s;
}

.btn-theme-toggle:hover {
    border-color: var(--accent);
    color: var(--accent);
}

.controls-bar select,
.controls-bar input[type="text"] {
    background: var(--input-bg);
    border: 1px solid var(--input-border);
    color: var(--text-primary);
    border-radius: 6px;
    padding: 0.4rem 0.6rem;
    font-size: 0.85rem;
    outline: none;
    transition: border-color 0.2s;
}

.controls-bar select:focus,
.controls-bar input[type="text"]:focus {
    border-color: var(--accent);
    box-shadow: 0 0 0 2px var(--accent-glow);
}

.search-box {
    position: relative;
    flex: 0 1 220px;
}

.search-box input { width: 100%; }

.search-dropdown {
    position: absolute;
    top: 100%;
    left: 0;
    right: 0;
    background: var(--tooltip-bg);
    border: 1px solid var(--border-color);
    border-radius: 6px;
    max-height: 250px;
    overflow-y: auto;
    display: none;
    z-index: 200;
    box-shadow: var(--shadow);
}

.search-dropdown.active { display: block; }

.search-dropdown a {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    padding: 0.5rem 0.75rem;
    color: var(--text-primary);
    text-decoration: none;
    font-size: 0.85rem;
    border-bottom: 1px solid var(--border-color);
}

.search-dropdown a:hover { background: var(--bg-card-hover); }
.search-dropdown a .symbol-badge {
    display: inline-block;
    width: 32px;
    text-align: center;
    font-weight: 700;
    font-family: 'Spectral', serif;
}

.filter-group { display: flex; align-items: center; gap: 0.4rem; }

.temperature-control {
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.temperature-control input[type="range"] {
    width: 140px;
    accent-color: var(--accent);
}

#temp-display {
    font-weight: 600;
    color: var(--accent);
    min-width: 50px;
    display: inline-block;
}

.btn-icon {
    background: transparent;
    border: 1px solid var(--border-color);
    color: var(--text-primary);
    border-radius: 6px;
    width: 36px;
    height: 36px;
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    transition: all 0.2s;
    font-size: 1.1rem;
}

.btn-icon:hover {
    background: var(--bg-card-hover);
    border-color: var(--accent);
    color: var(--accent);
}


/* ============================================================
   Periodic Table Grid
   ============================================================ */
.periodic-wrapper {
    max-width: 100%;
    overflow-x: auto;
    padding: 0;
}

.periodic-table {
    display: grid;
    grid-template-columns: repeat(18, minmax(62px, 1fr));
    grid-template-rows: repeat(10, auto);
    gap: 3px;
    padding: 1.5rem;
    max-width: 1440px;
    margin: 0 auto;
    min-width: 900px;
}


/* ============================================================
   Element Cell
   ============================================================ */
.element-cell {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: 5px;
    padding: 3px 4px;
    cursor: pointer;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    transition: transform 0.15s ease, box-shadow 0.15s ease, opacity 0.25s ease, border-color 0.2s;
    position: relative;
    min-height: 64px;
    user-select: none;
    border-left: 3px solid var(--cat-color, var(--border-color));
}

.element-cell:hover {
    transform: scale(1.4);
    z-index: 50;
    box-shadow: 0 0 24px var(--accent-glow), 0 8px 32px rgba(0,0,0,0.4);
    border-color: var(--accent);
}

.element-cell.dimmed {
    opacity: 0.1;
    pointer-events: none;
}

.element-cell.highlighted {
    border-color: var(--accent);
    box-shadow: 0 0 12px var(--accent-glow);
}

.element-cell .atomic-number {
    font-size: 0.55rem;
    color: var(--text-muted);
    position: absolute;
    top: 2px;
    left: 5px;
    line-height: 1;
}

.element-cell .symbol {
    font-family: 'Spectral', serif;
    font-size: 1.35rem;
    font-weight: 700;
    color: var(--text-primary);
    line-height: 1.2;
}

.element-cell .name {
    font-size: 0.48rem;
    color: var(--text-secondary);
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
    max-width: 100%;
    line-height: 1.2;
}

.element-cell .atomic-mass {
    font-size: 0.45rem;
    color: var(--text-muted);
    line-height: 1.2;
}

/* State of matter indicators */
.element-cell[data-current-state="gas"] {
    border-style: dashed;
    border-left-style: dashed;
}
.element-cell[data-current-state="liquid"] {
    border-bottom: 3px solid var(--accent);
}


/* ============================================================
   Legend
   ============================================================ */
.table-legend {
    display: flex;
    flex-wrap: wrap;
    gap: 0.5rem;
    padding: 0.75rem;
    background: var(--legend-bg);
    border-radius: 8px;
    border: 1px solid var(--border-color);
    align-items: center;
}

.legend-item {
    display: flex;
    align-items: center;
    gap: 0.3rem;
    font-size: 0.7rem;
    color: var(--text-secondary);
}

.legend-swatch {
    width: 12px;
    height: 12px;
    border-radius: 3px;
    border: 1px solid var(--border-color);
}

/* Gradient legend for property mode */
.legend-gradient {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    font-size: 0.7rem;
    color: var(--text-secondary);
}

.legend-gradient-bar {
    width: 120px;
    height: 12px;
    border-radius: 3px;
    background: linear-gradient(to right, hsl(240, 70%, 50%), hsl(120, 70%, 50%), hsl(0, 70%, 50%));
}


/* ============================================================
   Tooltip
   ============================================================ */
.element-tooltip {
    position: fixed;
    background: var(--tooltip-bg);
    border: 1px solid var(--border-color);
    border-radius: 10px;
    padding: 1rem;
    min-width: 240px;
    max-width: 300px;
    z-index: 1000;
    pointer-events: none;
    box-shadow: var(--shadow);
    transition: opacity 0.15s;
}

.element-tooltip.hidden { display: none; }

.element-tooltip .tt-header {
    display: flex;
    align-items: center;
    gap: 0.75rem;
    margin-bottom: 0.5rem;
}

.element-tooltip .tt-symbol {
    font-family: 'Spectral', serif;
    font-size: 2rem;
    font-weight: 700;
    width: 50px;
    height: 50px;
    display: flex;
    align-items: center;
    justify-content: center;
    border-radius: 8px;
    border: 2px solid var(--border-color);
}

.element-tooltip .tt-name {
    font-size: 1rem;
    font-weight: 600;
}

.element-tooltip .tt-number {
    font-size: 0.8rem;
    color: var(--text-secondary);
}

.element-tooltip .tt-props {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 0.25rem 1rem;
    font-size: 0.75rem;
}

.element-tooltip .tt-prop-label {
    color: var(--text-muted);
}

.element-tooltip .tt-prop-value {
    color: var(--text-primary);
    font-weight: 500;
}


/* ============================================================
   Lanthanide/Actinide Labels
   ============================================================ */
.series-label {
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 0.65rem;
    color: var(--text-muted);
    font-weight: 500;
    text-align: center;
}


/* ============================================================
   Page Hero (shared across pages)
   ============================================================ */
.page-hero {
    text-align: center;
    padding: 3rem 1rem 2rem;
    background: linear-gradient(180deg, var(--bg-secondary) 0%, var(--bg-primary) 100%);
}

.page-hero h1 {
    font-size: 2.2rem;
    font-weight: 700;
    margin-bottom: 0.5rem;
}

.page-hero p {
    font-size: 1.1rem;
    color: var(--text-secondary);
    max-width: 600px;
    margin: 0 auto;
}


/* ============================================================
   Element Detail Page
   ============================================================ */
.element-hero {
    display: flex;
    align-items: center;
    gap: 2rem;
    padding: 2rem;
    background: var(--bg-secondary);
    border-radius: 12px;
    border: 1px solid var(--border-color);
    margin-bottom: 2rem;
}

.element-hero .hero-symbol {
    font-family: 'Spectral', serif;
    font-size: 5rem;
    font-weight: 700;
    width: 140px;
    height: 140px;
    display: flex;
    align-items: center;
    justify-content: center;
    border-radius: 16px;
    border: 3px solid var(--border-color);
    flex-shrink: 0;
}

.element-hero .hero-info h1 {
    font-size: 2rem;
    margin-bottom: 0.25rem;
}

.element-hero .hero-meta {
    display: flex;
    gap: 1rem;
    flex-wrap: wrap;
    margin-top: 0.5rem;
}

.hero-meta .badge-custom {
    display: inline-block;
    padding: 0.3rem 0.8rem;
    border-radius: 20px;
    font-size: 0.8rem;
    font-weight: 500;
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    color: var(--text-secondary);
}

.property-cards {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 1.5rem;
    margin-bottom: 2rem;
}

.property-card {
    background: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: 12px;
    padding: 1.5rem;
}

.property-card h3 {
    font-size: 1rem;
    font-weight: 600;
    margin-bottom: 1rem;
    color: var(--accent);
}

.property-card table {
    width: 100%;
    font-size: 0.9rem;
}

.property-card table td {
    padding: 0.35rem 0;
    border-bottom: 1px solid var(--border-color);
}

.property-card table td:first-child {
    color: var(--text-secondary);
    width: 50%;
}

.property-card table td:last-child {
    font-weight: 500;
}


/* ============================================================
   Electron Shell Visualization
   ============================================================ */
.electron-shell-container {
    width: 280px;
    height: 280px;
    margin: 0 auto;
}

.electron-shell-container svg {
    width: 100%;
    height: 100%;
}

.electron-orbit {
    fill: none;
    stroke: var(--border-color);
    stroke-width: 1;
}

.electron-dot {
    fill: var(--accent);
}

.nucleus-text {
    fill: var(--text-primary);
    font-family: 'Spectral', serif;
    font-weight: 700;
    text-anchor: middle;
    dominant-baseline: central;
}


/* ============================================================
   Element Navigation
   ============================================================ */
.element-nav {
    display: flex;
    justify-content: space-between;
    margin-top: 2rem;
    padding-top: 1.5rem;
    border-top: 1px solid var(--border-color);
}

.element-nav a {
    color: var(--accent);
    text-decoration: none;
    font-weight: 500;
    display: flex;
    align-items: center;
    gap: 0.4rem;
}

.element-nav a:hover { text-decoration: underline; }


/* ============================================================
   Compare Page
   ============================================================ */
.compare-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 1.5rem;
}

.compare-card {
    background: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: 12px;
    padding: 1.5rem;
    text-align: center;
}

.compare-card .compare-symbol {
    font-family: 'Spectral', serif;
    font-size: 3rem;
    font-weight: 700;
}

.radar-container {
    max-width: 500px;
    margin: 2rem auto;
}


/* ============================================================
   Quiz Page
   ============================================================ */
.quiz-container {
    max-width: 600px;
    margin: 0 auto;
    background: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: 16px;
    padding: 2rem;
}

.quiz-score {
    display: flex;
    gap: 2rem;
    justify-content: center;
    margin-bottom: 1.5rem;
}

.quiz-score .stat {
    text-align: center;
}

.quiz-score .stat-value {
    font-size: 2rem;
    font-weight: 700;
    color: var(--accent);
}

.quiz-score .stat-label {
    font-size: 0.8rem;
    color: var(--text-secondary);
}

.quiz-question {
    font-size: 1.2rem;
    font-weight: 600;
    text-align: center;
    margin-bottom: 1.5rem;
}

.quiz-choices {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 0.75rem;
}

.quiz-choice {
    padding: 0.75rem 1rem;
    background: var(--bg-card);
    border: 2px solid var(--border-color);
    border-radius: 10px;
    cursor: pointer;
    text-align: center;
    font-weight: 500;
    transition: all 0.2s;
    color: var(--text-primary);
}

.quiz-choice:hover {
    border-color: var(--accent);
    background: var(--bg-card-hover);
}

.quiz-choice.correct {
    border-color: var(--success);
    background: var(--success-bg);
}

.quiz-choice.incorrect {
    border-color: var(--danger);
    background: var(--danger-bg);
}

.quiz-clue {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: 8px;
    padding: 0.75rem 1rem;
    margin-bottom: 0.5rem;
    font-size: 0.9rem;
    color: var(--text-secondary);
    opacity: 0;
    transform: translateY(10px);
    transition: all 0.3s;
}

.quiz-clue.revealed {
    opacity: 1;
    transform: translateY(0);
}


/* ============================================================
   Timeline Page
   ============================================================ */
.timeline-container {
    overflow-x: auto;
    padding: 2rem 1rem;
}

.timeline-svg {
    min-width: 100%;
}

.timeline-dot {
    cursor: pointer;
    transition: r 0.2s;
}

.timeline-dot:hover { r: 8; }

.timeline-label {
    font-size: 10px;
    fill: var(--text-secondary);
}

.timeline-year-label {
    font-size: 11px;
    fill: var(--text-muted);
}


/* ============================================================
   Trends Page
   ============================================================ */
.trends-controls {
    display: flex;
    gap: 1rem;
    align-items: center;
    margin-bottom: 1.5rem;
    flex-wrap: wrap;
}

.mini-table {
    display: grid;
    grid-template-columns: repeat(18, 1fr);
    grid-template-rows: repeat(10, 1fr);
    gap: 1px;
    max-width: 900px;
    margin: 0 auto;
}

.mini-cell {
    width: 100%;
    aspect-ratio: 1;
    border-radius: 2px;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 0.5rem;
    font-weight: 600;
    cursor: pointer;
    transition: transform 0.1s;
    color: var(--text-primary);
}

.mini-cell:hover {
    transform: scale(1.5);
    z-index: 10;
}


/* ============================================================
   Responsive
   ============================================================ */
@media (max-width: 1200px) {
    .periodic-table {
        grid-template-columns: repeat(18, minmax(48px, 1fr));
        padding: 1rem;
    }
    .element-cell { min-height: 55px; }
    .element-cell .symbol { font-size: 1.1rem; }
}

@media (max-width: 992px) {
    .periodic-table {
        grid-template-columns: repeat(18, minmax(36px, 1fr));
        gap: 2px;
    }
    .element-cell { min-height: 44px; padding: 2px; }
    .element-cell .name { display: none; }
    .element-cell .atomic-mass { display: none; }
    .element-cell .symbol { font-size: 0.95rem; }
    .element-cell .atomic-number { font-size: 0.5rem; }
    .controls-bar { gap: 0.5rem; padding: 0.5rem; }
    .element-hero { flex-direction: column; text-align: center; }

    .footer-top {
        grid-template-columns: repeat(2, 1fr);
    }
}

@media (max-width: 768px) {
    .brand-text {
        font-size: 0.95rem;
        max-width: 200px;
    }

    .brand-tld {
        display: none;
    }

    .page-hero h1 {
        font-size: 1.5rem;
    }

    .page-hero p {
        font-size: 0.95rem;
    }

    .temperature-control {
        min-width: 150px;
    }

    .auth-card {
        margin: 1.5rem 1rem;
        padding: 1.75rem 1.25rem;
    }

    .pricing-grid {
        grid-template-columns: 1fr;
        padding: 1rem;
    }

    .account-page {
        padding: 1.5rem 1rem;
    }

    .page-content {
        padding: 1.5rem 1rem;
    }

    .legal-content {
        padding: 1.5rem 1rem;
    }

    .footer-top {
        grid-template-columns: 1fr;
        gap: 1.5rem;
    }
}

@media (max-width: 576px) {
    .brand-text {
        font-size: 0.85rem;
        max-width: 160px;
    }

    .page-hero h1 {
        font-size: 1.25rem;
    }

    .periodic-table {
        grid-template-columns: repeat(18, minmax(22px, 1fr));
        gap: 1px;
        padding: 0.5rem;
        min-width: 0;
    }
    .element-cell { min-height: 28px; border-left-width: 2px; border-radius: 2px; }
    .element-cell .atomic-number { display: none; }
    .element-cell .symbol { font-size: 0.6rem; }
    .element-cell:hover { transform: scale(1.8); }
    .controls-bar { flex-direction: column; align-items: stretch; }
    .search-box { flex: 1 1 100%; }
    .temperature-control { min-width: 0; max-width: 100%; }
    .temperature-control input[type="range"] { width: 100px; }
    .filter-group { width: 100%; }
    .filter-group select { flex: 1; }
    .quiz-choices { grid-template-columns: 1fr; }

    .checkout-form {
        margin: 1rem;
        padding: 1.25rem;
    }
}


/* ============================================================
   Utility
   ============================================================ */
.hidden { display: none !important; }
.text-accent { color: var(--accent); }
.bg-card { background: var(--bg-card); }