:root {
  --bg: #FFFFFF; --band: #F5F8FC; --surface: #F7F9FC; --border: #E1E7F0;
  --text: #18212F; --muted: #5B6678; --accent: #1F51A8; --accent-hover: #17407F;
  --accent-text: #1F51A8; --tint: #E9F0FB; --on-accent: #FFFFFF;
  --danger: #B42318; --danger-tint: #FDECEA; --ok: #146C43; --ok-tint: #E3F4EA;
  --warn: #8A4B00; --warn-tint: #FFF1DD;
}
@media (prefers-color-scheme: dark) {
  :root {
    --bg: #0D1829; --band: #112038; --surface: #14243D; --border: #233957;
    --text: #E8EEF7; --muted: #A6B3C7; --accent: #2D62C4; --accent-hover: #3A71D6;
    --accent-text: #8FB2F0; --tint: #19305A; --on-accent: #FFFFFF;
    --danger: #FF8A80; --danger-tint: #3A1A1A; --ok: #7FD1A3; --ok-tint: #143326;
    --warn: #FFC37A; --warn-tint: #3A2A12;
  }
}
* { box-sizing: border-box; }
html, body { margin: 0; }
body { background: var(--band); color: var(--text); font-family: 'Source Sans 3', system-ui, sans-serif; font-size: 17px; line-height: 1.55; }
h1, h2, h3, .btn, .wordmark, .tab, .label { font-family: 'Archivo', system-ui, sans-serif; }
h1, h2, h3 { margin: 0; letter-spacing: -0.02em; line-height: 1.2; }
h1 { font-size: 30px; }
h2 { font-size: 22px; }
h3 { font-size: 18px; }
p { margin: 0; }
a { color: var(--accent-text); }
button { font: inherit; }
.boot { padding: 80px 20px; text-align: center; color: var(--muted); }

.wrap { max-width: 960px; margin: 0 auto; padding: 0 20px; }
.topbar { background: var(--bg); border-bottom: 1px solid var(--border); position: sticky; top: 0; z-index: 5; }
.topbar-row { display: flex; align-items: center; gap: 16px; min-height: 64px; flex-wrap: wrap; padding: 8px 0; }
.wordmark { font-weight: 700; font-size: 20px; letter-spacing: -0.02em; text-decoration: none; color: var(--text); }
.wordmark span { color: var(--accent-text); }
.wordmark small { font-family: 'Source Sans 3', sans-serif; font-weight: 600; font-size: 14px; color: var(--muted); letter-spacing: 0; margin-left: 8px; }
.topbar-right { margin-left: auto; display: flex; align-items: center; gap: 12px; flex-wrap: wrap; }
.who { color: var(--muted); font-size: 15px; overflow-wrap: anywhere; }
.tabs { display: flex; gap: 4px; flex-wrap: wrap; border-top: 1px solid var(--border); padding: 8px 0; }
.tab { padding: 8px 14px; border-radius: 8px; text-decoration: none; color: var(--muted); font-weight: 600; font-size: 15px; }
.tab:hover { color: var(--accent-text); background: var(--tint); }
.tab[aria-current="page"] { color: var(--accent-text); background: var(--tint); }

main { padding: 32px 0 80px; }
.stack { display: flex; flex-direction: column; gap: 24px; }
.panel { background: var(--bg); border: 1px solid var(--border); border-radius: 12px; padding: 24px; }
.panel > h2 + *, .panel > .panel-head + * { margin-top: 16px; }
.panel-head { display: flex; align-items: center; justify-content: space-between; gap: 12px; flex-wrap: wrap; }
.muted { color: var(--muted); }
.small { font-size: 15px; }
.back { display: inline-block; margin-bottom: 16px; text-decoration: none; font-weight: 600; font-size: 15px; }

.btn { display: inline-flex; align-items: center; justify-content: center; gap: 8px; min-height: 44px; padding: 10px 18px;
  border-radius: 8px; font-weight: 600; font-size: 15px; border: 1px solid var(--accent); cursor: pointer; text-decoration: none;
  background: var(--accent); color: var(--on-accent); transition: background .15s, border-color .15s; }
.btn:hover { background: var(--accent-hover); border-color: var(--accent-hover); color: var(--on-accent); }
.btn:disabled { opacity: .55; cursor: default; }
.btn.secondary { background: transparent; color: var(--accent-text); border-color: var(--accent-text); }
.btn.secondary:hover { background: var(--tint); }
.btn.ghost { background: transparent; border-color: transparent; color: var(--accent-text); padding: 10px 12px; }
.btn.ghost:hover { background: var(--tint); }
.btn.danger { background: transparent; color: var(--danger); border-color: transparent; padding: 10px 12px; }
.btn.danger:hover { background: var(--danger-tint); }
.btn.small { min-height: 36px; padding: 6px 12px; font-size: 14px; }
.btn-row { display: flex; gap: 10px; flex-wrap: wrap; align-items: center; }

.field { display: flex; flex-direction: column; gap: 6px; }
.field label, .label { font-weight: 600; font-size: 15px; }
.hint { color: var(--muted); font-size: 14px; }
input[type=text], input[type=email], input[type=date], input[type=search], select, textarea {
  font: inherit; font-size: 16px; color: var(--text); background: var(--bg); border: 1px solid var(--border);
  border-radius: 8px; padding: 10px 12px; min-height: 44px; width: 100%; }
textarea { min-height: 140px; resize: vertical; line-height: 1.5; }
input:focus, select:focus, textarea:focus { outline: 2px solid var(--accent-text); outline-offset: 1px; border-color: var(--accent-text); }
.grid-2 { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 14px; }
.check { display: flex; align-items: center; gap: 10px; min-height: 36px; cursor: pointer; }
.check input { width: 18px; height: 18px; accent-color: var(--accent); }

.notice { border-radius: 10px; padding: 12px 14px; font-size: 15px; }
.notice.error { background: var(--danger-tint); color: var(--danger); }
.notice.ok { background: var(--ok-tint); color: var(--ok); }
.notice.info { background: var(--tint); color: var(--text); }

.list { display: flex; flex-direction: column; border: 1px solid var(--border); border-radius: 10px; overflow: hidden; background: var(--bg); }
.row { display: flex; align-items: center; gap: 14px; padding: 14px 16px; text-decoration: none; color: var(--text); flex-wrap: wrap; }
.row + .row { border-top: 1px solid var(--border); }
a.row:hover { background: var(--surface); }
.row-main { flex: 1 1 240px; min-width: 0; }
.row-title { font-weight: 600; overflow-wrap: anywhere; }
.row-meta { color: var(--muted); font-size: 14px; }
.empty { color: var(--muted); padding: 18px 16px; font-size: 15px; }

.badge { display: inline-flex; align-items: center; font-size: 13px; font-weight: 600; padding: 2px 10px; border-radius: 999px; background: var(--tint); color: var(--accent-text); white-space: nowrap; }
.badge.ok { background: var(--ok-tint); color: var(--ok); }
.badge.warn { background: var(--warn-tint); color: var(--warn); }
.badge.danger { background: var(--danger-tint); color: var(--danger); }
.badge.neutral { background: var(--surface); color: var(--muted); border: 1px solid var(--border); }

.decks { display: grid; grid-template-columns: repeat(auto-fill, minmax(240px, 1fr)); gap: 14px; }
.deck { background: var(--bg); border: 1px solid var(--border); border-radius: 12px; padding: 18px; display: flex; flex-direction: column; gap: 10px; }
.deck-counts { display: flex; gap: 8px; flex-wrap: wrap; }

/* login */
.login-wrap { min-height: 100vh; display: flex; align-items: center; justify-content: center; padding: 24px 16px; }
.login { width: 100%; max-width: 420px; background: var(--bg); border: 1px solid var(--border); border-radius: 14px; padding: 32px 28px; display: flex; flex-direction: column; gap: 18px; }
.login .wordmark { font-size: 22px; }
.code-input { font-family: 'Archivo', sans-serif !important; font-size: 26px !important; letter-spacing: 10px; text-align: center; }

/* content */
.content { overflow-wrap: anywhere; }
.content > * + * { margin-top: 12px; }
.content h1, .content h2, .content h3 { margin-top: 20px; }
.content ul, .content ol { padding-left: 22px; margin-bottom: 0; }
.content li + li { margin-top: 4px; }
.content code { background: var(--surface); border: 1px solid var(--border); border-radius: 4px; padding: 1px 5px; font-size: 15px; }
.content blockquote { margin-left: 0; padding-left: 14px; border-left: 3px solid var(--border); color: var(--muted); }
.files { display: flex; flex-direction: column; gap: 8px; }
.file { display: flex; align-items: center; gap: 10px; padding: 10px 14px; border: 1px solid var(--border); border-radius: 10px; background: var(--surface); flex-wrap: wrap; }
.file a { font-weight: 600; overflow-wrap: anywhere; }

/* study */
.study { max-width: 720px; margin: 0 auto; display: flex; flex-direction: column; gap: 18px; }
.study-top { display: flex; align-items: center; justify-content: space-between; gap: 12px; flex-wrap: wrap; }
.stage { position: relative; background: var(--bg); border: 1px solid var(--border); border-radius: 16px; min-height: 300px;
  padding: 40px 28px; display: flex; flex-direction: column; justify-content: center; gap: 24px; text-align: center;
  user-select: none; -webkit-user-select: none; -webkit-touch-callout: none; overflow: hidden; }
.stage .wm { position: absolute; inset: 0; pointer-events: none; opacity: .07; background-repeat: repeat; }
.face { position: relative; font-size: 22px; line-height: 1.45; white-space: pre-wrap; overflow-wrap: anywhere; }
.face.front { font-family: 'Archivo', sans-serif; font-weight: 600; font-size: 24px; }
.face.back { border-top: 1px solid var(--border); padding-top: 24px; font-size: 19px; }
.rate { display: grid; grid-template-columns: repeat(4, minmax(0, 1fr)); gap: 10px; }
.rate .btn { flex-direction: column; gap: 2px; min-height: 64px; line-height: 1.2; }
.rate .btn small { font-family: 'Source Sans 3', sans-serif; font-weight: 400; font-size: 13px; opacity: .85; }
.rate .again { background: transparent; color: var(--danger); border-color: var(--danger); }
.rate .again:hover { background: var(--danger-tint); }
.rate .hard { background: transparent; color: var(--warn); border-color: var(--warn); }
.rate .hard:hover { background: var(--warn-tint); }
.rate .good { background: var(--accent); }
.rate .easy { background: transparent; color: var(--ok); border-color: var(--ok); }
.rate .easy:hover { background: var(--ok-tint); }
.keys { text-align: center; color: var(--muted); font-size: 14px; }
.done-box { text-align: center; padding: 48px 24px; }
.done-box h2 { margin-bottom: 8px; }

/* admin */
.table-wrap { overflow-x: auto; border: 1px solid var(--border); border-radius: 10px; background: var(--bg); }
table { border-collapse: collapse; width: 100%; font-size: 15px; }
th, td { text-align: left; padding: 12px 14px; border-bottom: 1px solid var(--border); white-space: nowrap; }
th { font-family: 'Archivo', sans-serif; font-weight: 600; font-size: 14px; color: var(--muted); background: var(--surface); }
tr:last-child td { border-bottom: 0; }
td a { font-weight: 600; text-decoration: none; }
.card-row { display: grid; grid-template-columns: minmax(0, 1fr) minmax(0, 1.4fr) auto; gap: 12px; align-items: start; padding: 12px 16px; }
.card-row + .card-row { border-top: 1px solid var(--border); }
.card-row .f { font-weight: 600; white-space: pre-wrap; overflow-wrap: anywhere; }
.card-row .b { color: var(--muted); white-space: pre-wrap; overflow-wrap: anywhere; }
.card-row textarea { min-height: 70px; }
.students-pick { display: grid; grid-template-columns: repeat(auto-fill, minmax(220px, 1fr)); gap: 2px 16px; padding: 6px 0; }
.toast { position: fixed; left: 50%; bottom: 24px; transform: translateX(-50%); background: var(--text); color: var(--bg); padding: 10px 18px; border-radius: 10px; font-size: 15px; z-index: 50; box-shadow: 0 6px 20px rgba(0,0,0,.2); max-width: calc(100% - 32px); }
.preview { border: 1px dashed var(--border); border-radius: 10px; padding: 16px; background: var(--surface); }

@media (max-width: 640px) {
  main { padding: 20px 0 60px; }
  .panel { padding: 18px 16px; }
  h1 { font-size: 26px; }
  .grid-2 { grid-template-columns: minmax(0, 1fr); }
  .card-row { grid-template-columns: minmax(0, 1fr); }
  .rate { grid-template-columns: repeat(2, minmax(0, 1fr)); }
  .stage { min-height: 240px; padding: 28px 18px; }
  .face.front { font-size: 21px; }
  .face { font-size: 19px; }
}

@media (hover: none) { .keys { display: none; } }