:root {
    color-scheme: light;
    --bg: #f7f5ef;
    --surface: #ffffff;
    --text: #172033;
    --muted: #5c6473;
    --accent: #2457a6;
    --border: #d8dbe2;
    --code: #eef1f6;
    --shadow: rgba(23, 32, 51, 0.12);
}

:root[data-theme="dark"] {
    color-scheme: dark;
    --bg: #111318;
    --surface: #1b1e25;
    --text: #f4f5f7;
    --muted: #bdc2cc;
    --accent: #8eb7ff;
    --border: #414651;
    --code: #0c1018;
    --shadow: rgba(0, 0, 0, 0.35);
}

* { box-sizing: border-box; }

body {
    min-height: 100vh;
    margin: 0;
    background: var(--bg);
    color: var(--text);
    font-family: "Atkinson Hyperlegible", "Segoe UI", system-ui, sans-serif;
    line-height: 1.5;
}

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

.topbar {
    display: flex;
    justify-content: space-between;
    gap: 1rem;
    padding: 1rem clamp(1rem, 4vw, 3rem);
    border-bottom: 1px solid var(--border);
    color: var(--muted);
}

.topbar a { font-weight: 700; text-decoration: none; }

.overview {
    width: min(1050px, calc(100% - 2rem));
    margin: 0 auto;
    padding: clamp(3rem, 7vw, 6rem) 0;
}

.overview h1 { margin: 0; font-size: clamp(3rem, 7vw, 5.5rem); line-height: 1; }
.overview h2 { margin-top: 3.5rem; }
.intro { max-width: 55ch; font-size: 1.25rem; color: var(--muted); }
.eyebrow { color: var(--accent); font-weight: 800; }

.chapter-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(250px, 1fr)); gap: 1rem; }
.chapter-card {
    display: grid;
    gap: .55rem;
    padding: 1.4rem;
    border: 1px solid var(--border);
    border-radius: 14px;
    background: var(--surface);
    color: var(--text);
    text-decoration: none;
    box-shadow: 0 12px 30px var(--shadow);
}
.chapter-card:hover { border-color: var(--accent); transform: translateY(-2px); }
.chapter-number, .chapter-card > span:last-child { color: var(--muted); }

.random-card {
    display: grid;
    gap: 1.5rem;
    min-height: 430px;
    margin-top: 3rem;
    padding: clamp(1.5rem, 5vw, 3.5rem);
    border: 1px solid var(--border);
    border-radius: 18px;
    background: var(--surface);
    box-shadow: 0 12px 30px var(--shadow);
}
.random-card-meta, .random-actions { display: flex; align-items: center; justify-content: space-between; gap: 1rem; }
.random-card-meta { color: var(--muted); font-weight: 700; }
.random-card h2 { max-width: 24ch; margin: 0; font-size: clamp(2rem, 5vw, 4rem); line-height: 1.12; }
.random-answer { padding-top: 1.5rem; border-top: 1px solid var(--border); }
.random-answer p { max-width: 65ch; margin: 0; font-size: clamp(1.2rem, 2.5vw, 1.7rem); font-weight: 700; }
.random-answer pre { margin-top: 1.5rem; }
.random-actions { align-self: end; justify-content: flex-end; }

.deck-shell { min-height: 100vh; display: grid; grid-template-rows: auto 1fr auto; }
.deck { min-height: 0; position: relative; }
.slide { display: none; min-height: calc(100vh - 9rem); padding: clamp(2rem, 6vw, 5rem); place-items: center; }
.slide.is-active { display: grid; }
.slide-content { width: min(1050px, 100%); }
.slide h1 { max-width: 20ch; margin: 0; font-size: clamp(2.5rem, 5.5vw, 5.4rem); line-height: 1.08; }
.slide p { max-width: 65ch; font-size: clamp(1.15rem, 2vw, 1.7rem); }
.think-prompt { margin-top: 2.5rem; color: var(--muted); }
.answer-slide h1 { font-size: clamp(2rem, 4.3vw, 4.3rem); }
pre {
    width: min(760px, 100%);
    margin: 2rem 0 0;
    padding: 1.2rem 1.4rem;
    overflow-x: auto;
    border: 1px solid var(--border);
    border-radius: 12px;
    background: var(--code);
    font-size: clamp(1.15rem, 2vw, 1.65rem);
    box-shadow: 0 12px 30px var(--shadow);
}

.deck-footer { display: flex; align-items: center; justify-content: space-between; gap: 1rem; padding: .8rem clamp(1rem, 4vw, 3rem); border-top: 1px solid var(--border); }
.deck-footer p { margin: 0; color: var(--muted); text-align: center; }
button { padding: .75rem 1rem; border: 1px solid var(--border); border-radius: 9px; background: var(--surface); color: var(--text); font-weight: 700; cursor: pointer; }
button:hover:not(:disabled) { border-color: var(--accent); }
button:disabled { opacity: .4; cursor: not-allowed; }
kbd { padding: .15rem .4rem; border: 1px solid var(--border); border-radius: 5px; background: var(--surface); }
a:focus-visible, button:focus-visible { outline: 3px solid var(--accent); outline-offset: 3px; }

@media (max-width: 650px) {
    .deck-footer p { display: none; }
    .topbar { font-size: .9rem; }
}

@media (prefers-reduced-motion: no-preference) {
    .chapter-card { transition: transform 150ms ease, border-color 150ms ease; }
}