:root { --fg: #1b1f24; --bg: #f7f5f0; --accent: #1f3a5f; --muted: #5b6370; --card: #ffffff; }
@media (prefers-color-scheme: dark) { :root { --fg: #e9e6df; --bg: #15181c; --accent: #8fb3e0; --muted: #a4abb5; --card: #1f2329; } }
* { box-sizing: border-box; }
body { margin: 0; background: var(--bg); color: var(--fg); font: 16px/1.7 system-ui, -apple-system, "Hiragino Sans", "Noto Sans JP", sans-serif; }
main { max-width: 560px; margin: 0 auto; padding: calc(16px + env(safe-area-inset-top)) 16px calc(24px + env(safe-area-inset-bottom)); }
h1 { font-size: 1.4rem; color: var(--accent); margin: 0 0 .25rem; }
h2 { font-size: 1rem; margin: 0 0 .5rem; }
section { background: var(--card); border-radius: 12px; padding: 16px; margin: 12px 0; }
.note, dt { color: var(--muted); font-size: .9rem; }
dl { margin: 0; } dd { margin: 0 0 .5rem; word-break: break-all; }
label { display: block; margin: .75rem 0 .25rem; }
input { width: 100%; padding: 12px; font-size: 16px; border: 1px solid var(--muted); border-radius: 8px; background: transparent; color: var(--fg); }
button { width: 100%; margin-top: .75rem; padding: 12px; font-size: 16px; border: 0; border-radius: 8px; background: var(--accent); color: var(--bg); }
#message { min-height: 1.5em; }
[hidden] { display: none !important; }
textarea { width: 100%; padding: 12px; font: inherit; font-size: 16px; border: 1px solid var(--muted); border-radius: 8px; background: transparent; color: var(--fg); resize: vertical; }
label.check { display: flex; gap: .5rem; align-items: flex-start; }
label.check input { width: auto; margin-top: .4rem; }
a.button { display: block; text-align: center; text-decoration: none; margin-top: .75rem; padding: 12px; border-radius: 8px; background: var(--accent); color: var(--bg); }
button.secondary, a.button.secondary { background: transparent; color: var(--accent); border: 1px solid var(--accent); }
button.danger { background: #b3261e; color: #fff; }
button:disabled { opacity: .55; }
.videos ul { list-style: none; margin: 0; padding: 0; }
.videos li { margin-bottom: .5rem; }
.chapter h3 { font-size: .95rem; margin: 1rem 0 .25rem; color: var(--accent); }
.videos button { text-align: left; }
#player iframe { width: 100%; aspect-ratio: 16 / 9; border: 0; border-radius: 8px; margin-top: .75rem; }
details { margin-top: 1rem; } summary { color: var(--muted); cursor: pointer; }
footer { margin-top: 1.5rem; text-align: center; }
footer a { color: var(--muted); }

/* 動画の登録画面（/admin） */
main.wide { max-width: 760px; }
.admin-video { border: 1px solid #d0d7e2; border-radius: 8px; padding: 12px; margin: 12px 0; }