.igcse-study-app {
    --igcse-blue: #1d2a8c;
    --igcse-gold: #f2b233;
    --igcse-ink: #252b3a;
    --igcse-soft: #eef3ff;
    --igcse-line: #dfe4f4;
    color: var(--igcse-ink);
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Arial, sans-serif;
    line-height: 1.6;
    max-width: 980px;
    margin: 0 auto;
    padding: 18px;
}

.igcse-site-header {
    align-items: center;
    display: flex;
    gap: 18px;
    justify-content: space-between;
    margin-bottom: 16px;
}

.igcse-brand {
    align-items: center;
    color: var(--igcse-blue);
    display: inline-flex;
    font-weight: 900;
    gap: 10px;
    text-decoration: none;
}

.igcse-brand-mark {
    align-items: center;
    background: var(--igcse-blue);
    border-radius: 8px;
    color: #fff;
    display: inline-flex;
    height: 36px;
    justify-content: center;
    width: 36px;
}

.igcse-site-nav,
.igcse-footer nav {
    display: flex;
    flex-wrap: wrap;
    gap: 12px;
}

.igcse-site-nav a,
.igcse-footer a {
    color: var(--igcse-blue);
    font-size: 0.92rem;
    font-weight: 800;
    text-decoration: none;
}

.igcse-hero {
    align-items: end;
    background: linear-gradient(135deg, #111a55, #2537a6 58%, #f2b233);
    border-radius: 8px;
    color: #fff;
    display: grid;
    gap: 22px;
    grid-template-columns: minmax(0, 1fr) 190px;
    margin-bottom: 18px;
    padding: 28px;
}

.igcse-eyebrow,
.igcse-topic-header span,
.igcse-simulation header span {
    font-size: 0.76rem;
    font-weight: 800;
    letter-spacing: 0.06em;
    text-transform: uppercase;
}

.igcse-hero h1 {
    font-size: clamp(2rem, 6vw, 3.8rem);
    line-height: 1;
    margin: 8px 0;
}

.igcse-hero-copy p {
    max-width: 620px;
}

.igcse-hero-actions {
    display: flex;
    flex-wrap: wrap;
    gap: 10px;
    margin-top: 18px;
}

.igcse-hero-actions a {
    background: #fff;
    border-radius: 999px;
    color: var(--igcse-blue);
    font-weight: 900;
    padding: 10px 14px;
    text-decoration: none;
}

.igcse-hero-actions a + a {
    background: rgba(255, 255, 255, 0.16);
    color: #fff;
}

.igcse-hero-panel {
    background: rgba(255, 255, 255, 0.14);
    border: 1px solid rgba(255, 255, 255, 0.24);
    border-radius: 8px;
    display: grid;
    gap: 4px;
    padding: 16px;
}

.igcse-hero-panel strong {
    font-size: 2.2rem;
    line-height: 1;
}

.igcse-hero-panel span {
    font-weight: 800;
    opacity: 0.82;
}

.igcse-section {
    margin: 26px 0;
}

.igcse-section-header {
    margin-bottom: 14px;
}

.igcse-section-header h2 {
    color: var(--igcse-blue);
    font-size: clamp(1.7rem, 4vw, 2.5rem);
    margin: 4px 0;
}

.igcse-section-header p {
    max-width: 720px;
}

.igcse-chapter-grid {
    display: grid;
    gap: 12px;
    grid-template-columns: repeat(auto-fit, minmax(235px, 1fr));
}

.igcse-chapter-card {
    background: #fff;
    border: 1px solid var(--igcse-line);
    border-radius: 8px;
    box-shadow: 0 8px 22px rgba(15, 25, 70, 0.05);
    display: flex;
    flex-direction: column;
    gap: 8px;
    min-height: 205px;
    padding: 16px;
}

.igcse-chapter-number {
    color: var(--igcse-gold);
    font-size: 0.76rem;
    font-weight: 900;
    text-transform: uppercase;
}

.igcse-chapter-card h3 {
    color: var(--igcse-blue);
    font-size: 1.24rem;
    margin: 0;
}

.igcse-chapter-card p {
    margin: 0;
}

.igcse-card-footer {
    align-items: center;
    display: flex;
    justify-content: space-between;
    margin-top: auto;
}

.igcse-card-footer span {
    color: #70778a;
    font-size: 0.84rem;
    font-weight: 800;
}

.igcse-card-footer a {
    background: var(--igcse-soft);
    border-radius: 999px;
    color: var(--igcse-blue);
    font-size: 0.86rem;
    font-weight: 900;
    padding: 8px 11px;
    text-decoration: none;
}

.igcse-chapter-detail {
    background: #f8faff;
    border: 1px solid var(--igcse-line);
    border-radius: 8px;
    padding: 18px;
}

.igcse-topic-grid {
    display: grid;
    gap: 10px;
    grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
}

.igcse-topic-link {
    background: #fff;
    border: 1px solid var(--igcse-line);
    border-radius: 8px;
    color: var(--igcse-ink);
    display: grid;
    gap: 5px;
    min-height: 122px;
    padding: 13px;
    text-decoration: none;
}

.igcse-topic-link span {
    color: var(--igcse-gold);
    font-size: 0.76rem;
    font-weight: 900;
}

.igcse-topic-link strong {
    color: var(--igcse-blue);
    font-size: 1rem;
}

.igcse-topic-link em {
    align-self: end;
    color: #70778a;
    font-size: 0.82rem;
    font-style: normal;
    font-weight: 800;
}

.igcse-topic-link.is-live {
    border-color: rgba(29, 42, 140, 0.42);
    box-shadow: 0 10px 24px rgba(29, 42, 140, 0.10);
}

.igcse-topic-link.is-live em {
    color: var(--igcse-blue);
}

.igcse-topic-card {
    background: #fff;
    border: 1px solid var(--igcse-line);
    border-radius: 8px;
    box-shadow: 0 8px 22px rgba(15, 25, 70, 0.06);
    padding: 20px;
}

.igcse-topic-nav {
    display: flex;
    flex-wrap: wrap;
    gap: 10px;
    justify-content: space-between;
    margin: 12px 0 18px;
}

.igcse-topic-nav a {
    background: var(--igcse-soft);
    border-radius: 999px;
    color: var(--igcse-blue);
    font-size: 0.88rem;
    font-weight: 900;
    padding: 9px 12px;
    text-decoration: none;
}

.igcse-topic-nav.is-bottom {
    border-top: 1px solid var(--igcse-line);
    margin-bottom: 0;
    margin-top: 20px;
    padding-top: 14px;
}

.igcse-topic-header {
    border-bottom: 1px solid var(--igcse-line);
    margin-bottom: 16px;
}

.igcse-topic-header h2,
.igcse-note-section h3,
.igcse-simulation h3 {
    color: var(--igcse-blue);
}

.igcse-note-section {
    margin: 18px 0;
}

.igcse-equation {
    background: var(--igcse-soft);
    border-radius: 8px;
    color: var(--igcse-blue);
    font-family: "SFMono-Regular", Consolas, monospace;
    font-weight: 700;
    margin: 10px 0;
    padding: 11px 12px;
}

.igcse-table-wrap {
    overflow-x: auto;
}

.igcse-table {
    border-collapse: collapse;
    width: 100%;
}

.igcse-table th {
    background: var(--igcse-blue);
    color: #fff;
}

.igcse-table th,
.igcse-table td {
    border: 1px solid var(--igcse-line);
    padding: 10px;
    text-align: left;
    vertical-align: top;
}

.igcse-principle-grid {
    display: grid;
    gap: 10px;
    grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
}

.igcse-principle-grid div {
    background: var(--igcse-soft);
    border-radius: 8px;
    padding: 12px;
}

.igcse-principle-grid strong {
    color: var(--igcse-blue);
}

.igcse-principle-grid p {
    margin-bottom: 0;
}

.igcse-simulation {
    background: linear-gradient(180deg, #fff, #f8faff);
    border: 1px solid var(--igcse-line);
    border-radius: 8px;
    margin-top: 20px;
    padding: 14px;
}

.igcse-half-life-canvas,
.igcse-terminal-canvas,
.igcse-density-canvas {
    background: var(--igcse-soft);
    border-radius: 8px;
    display: block;
    height: auto;
    max-width: 100%;
    width: 100%;
}

.igcse-half-life-sim label,
.igcse-motion-sim label,
.igcse-density-sim label {
    color: var(--igcse-blue);
    display: grid;
    font-size: 0.9rem;
    font-weight: 800;
    gap: 8px;
    grid-template-columns: 160px 1fr 82px;
    margin-top: 12px;
}

.igcse-half-life-sim input,
.igcse-motion-sim input,
.igcse-density-sim input {
    accent-color: var(--igcse-blue);
    width: 100%;
}

.igcse-metric-grid {
    display: grid;
    gap: 10px;
    grid-template-columns: repeat(auto-fit, minmax(160px, 1fr));
    margin-top: 12px;
}

.igcse-metric-grid div {
    background: var(--igcse-soft);
    border-radius: 8px;
    padding: 10px;
}

.igcse-metric-grid span {
    color: #70778a;
    display: block;
    font-size: 0.74rem;
    font-weight: 800;
    text-transform: uppercase;
}

.igcse-metric-grid strong {
    color: var(--igcse-blue);
}

.igcse-footer {
    align-items: start;
    border-top: 1px solid var(--igcse-line);
    display: flex;
    gap: 18px;
    justify-content: space-between;
    margin-top: 30px;
    padding: 20px 0 4px;
}

.igcse-footer p {
    color: #70778a;
    margin: 10px 0 0;
}

@media (max-width: 640px) {
    .igcse-study-app {
        padding: 10px;
    }

    .igcse-hero,
    .igcse-topic-card {
        padding: 16px;
    }

    .igcse-site-header,
    .igcse-footer {
        align-items: flex-start;
        flex-direction: column;
    }

    .igcse-hero {
        grid-template-columns: 1fr;
    }

    .igcse-half-life-sim label,
    .igcse-motion-sim label,
    .igcse-density-sim label {
        grid-template-columns: 1fr;
    }
}