/* ── AI Practice ──────────────────────────────────────────────────────────
   Type: one superfamily (IBM Plex Sans / Sans SC / Mono / Serif) so Latin
   terminology and Chinese prose share a skeleton instead of clashing.
   Color: a single sequential ramp encodes SRS consolidation (pale = new,
   deep = mastered); ember and jade are reserved strictly for feedback.
   ───────────────────────────────────────────────────────────────────────── */

:root {
  --ink:        #171B2E;
  --ink-soft:   #4C5370;
  --ink-faint:  #8890A8;
  --paper:      #F4F5F8;
  --card:       #FFFFFF;
  --line:       #E4E6ED;
  --line-soft:  #EFF1F5;

  --violet:      #5A48E0;
  --violet-deep: #3A2CAC;
  --violet-soft: #EEEBFD;
  --ember:       #D9482A;
  --ember-soft:  #FCEDE8;
  --jade:        #0B8F69;
  --jade-soft:   #E4F5EF;

  /* consolidation ramp — pale to deep reads as "settling into memory" */
  --s-new:      #D6D9E3;
  --s-learning: #B2A5F2;
  --s-review:   #7460E6;
  --s-mastered: #3A2CAC;

  --sans: "IBM Plex Sans", "IBM Plex Sans SC", "PingFang SC", "Microsoft YaHei",
          "Noto Sans CJK SC", system-ui, sans-serif;
  --mono: "IBM Plex Mono", ui-monospace, "Cascadia Mono", Menlo, monospace;
  --serif: "IBM Plex Serif", "Songti SC", Georgia, serif;

  --r-sm: 8px;
  --r-md: 14px;
  --r-lg: 20px;
  --shadow: 0 1px 2px rgba(23,27,46,.05), 0 8px 24px -12px rgba(23,27,46,.18);
  --tap: 52px;
  --ease: cubic-bezier(.32,.72,.26,1);
}

@media (prefers-color-scheme: dark) {
  :root {
    --ink:       #ECEEF5;
    --ink-soft:  #A7AEC6;
    --ink-faint: #757D97;
    --paper:     #12151F;
    --card:      #1A1E2C;
    --line:      #2A3043;
    --line-soft: #232838;

    --violet:      #8B7BFF;
    --violet-deep: #B6ABFF;
    --violet-soft: #262244;
    --ember:       #FF7A5C;
    --ember-soft:  #35211D;
    --jade:        #35C79A;
    --jade-soft:   #14302A;

    --s-new:      #333A50;
    --s-learning: #5B4CA8;
    --s-review:   #7F6DEE;
    --s-mastered: #B6ABFF;
    --shadow: 0 1px 2px rgba(0,0,0,.3), 0 8px 24px -12px rgba(0,0,0,.6);
  }
}

* { box-sizing: border-box; }

html, body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font-family: var(--sans);
  font-size: 16px;
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
  -webkit-text-size-adjust: 100%;
}

button, input { font: inherit; color: inherit; }
a { color: inherit; text-decoration: none; }

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

:focus-visible {
  outline: 2px solid var(--violet);
  outline-offset: 2px;
  border-radius: 4px;
}

/* ── Boot ────────────────────────────────────────────────────────────── */
.boot { display: grid; place-items: center; min-height: 100dvh; }
.boot-dot {
  width: 10px; height: 10px; border-radius: 50%;
  background: var(--violet);
  animation: pulse 1s var(--ease) infinite;
}
@keyframes pulse { 50% { opacity: .25; transform: scale(.7); } }

/* ── Shell ───────────────────────────────────────────────────────────── */
.app { min-height: 100dvh; display: flex; flex-direction: column; }

.topbar {
  position: sticky; top: 0; z-index: 20;
  display: flex; align-items: center; gap: 20px;
  padding: 14px 20px;
  background: color-mix(in srgb, var(--paper) 88%, transparent);
  backdrop-filter: saturate(1.4) blur(12px);
  border-bottom: 1px solid var(--line);
}

.wordmark {
  font-family: var(--mono);
  font-weight: 600;
  font-size: .82rem;
  letter-spacing: .12em;
  text-transform: uppercase;
  white-space: nowrap;
}
.wordmark::before {
  content: ""; display: inline-block; vertical-align: -1px;
  width: 7px; height: 12px; margin-right: 9px; border-radius: 2px;
  background: linear-gradient(var(--s-learning), var(--s-mastered));
}

.railnav { display: none; gap: 4px; margin-left: auto; }
.railnav a {
  font-size: .9rem; padding: 7px 14px; border-radius: 999px;
  color: var(--ink-soft); transition: background .18s, color .18s;
}
.railnav a:hover { background: var(--line-soft); color: var(--ink); }
.railnav a[aria-current] { background: var(--ink); color: var(--paper); }

.userchip {
  margin-left: auto;
  display: flex; align-items: center; gap: 8px;
  padding: 6px 8px 6px 14px;
  background: none; border: 1px solid var(--line); border-radius: 999px;
  font-size: .85rem; cursor: pointer;
  transition: border-color .18s;
}
.railnav:not(:empty) ~ .userchip { margin-left: 0; }
.userchip:hover { border-color: var(--ink-faint); }
.userchip span {
  display: grid; place-items: center;
  width: 26px; height: 26px; border-radius: 50%;
  background: var(--violet); color: #fff;
  font-size: .72rem; font-weight: 600;
}

.view {
  flex: 1;
  width: 100%; max-width: 760px; margin: 0 auto;
  padding: 26px 20px calc(96px + env(safe-area-inset-bottom));
}

.tabbar {
  position: fixed; inset: auto 0 0 0; z-index: 20;
  display: grid; grid-auto-flow: column; grid-auto-columns: 1fr;
  padding: 6px 8px calc(6px + env(safe-area-inset-bottom));
  background: color-mix(in srgb, var(--card) 92%, transparent);
  backdrop-filter: blur(12px);
  border-top: 1px solid var(--line);
}
.tabbar a {
  display: grid; justify-items: center; gap: 3px;
  padding: 7px 0; border-radius: var(--r-sm);
  font-size: .68rem; color: var(--ink-faint);
  font-family: var(--mono); letter-spacing: .04em;
}
.tabbar a svg { width: 21px; height: 21px; stroke-width: 1.6; }
.tabbar a[aria-current] { color: var(--violet); }
.tabbar .badge {
  position: absolute; transform: translate(14px, -4px);
  min-width: 16px; height: 16px; padding: 0 4px;
  border-radius: 999px; background: var(--ember); color: #fff;
  font-size: .6rem; line-height: 16px; text-align: center;
}

body.focusmode .topbar, body.focusmode .tabbar { display: none; }
body.focusmode .view { padding-top: 0; max-width: 660px; }

/* ── Type ────────────────────────────────────────────────────────────── */
.eyebrow {
  font-family: var(--mono); font-size: .72rem; font-weight: 500;
  letter-spacing: .14em; text-transform: uppercase; color: var(--ink-faint);
}
h1 { font-size: 1.45rem; font-weight: 600; letter-spacing: -.01em; margin: 0; }
h2 { font-size: 1.02rem; font-weight: 600; margin: 0; }
.muted { color: var(--ink-soft); }
.mono { font-family: var(--mono); }
.num {
  font-family: var(--serif); font-weight: 700;
  letter-spacing: -.03em; font-variant-numeric: tabular-nums;
}

/* ── Cards & buttons ─────────────────────────────────────────────────── */
.card {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: var(--r-lg);
  padding: 20px;
}
.stack { display: grid; gap: 14px; }
.row { display: flex; align-items: center; gap: 10px; }
.spread { display: flex; align-items: center; justify-content: space-between; gap: 12px; }

.btn {
  display: flex; align-items: center; justify-content: center; gap: 8px;
  min-height: var(--tap); padding: 0 22px;
  border: 1px solid transparent; border-radius: var(--r-md);
  background: var(--ink); color: var(--paper);
  font-size: 1rem; font-weight: 500; cursor: pointer;
  transition: transform .12s var(--ease), opacity .18s, background .18s;
}
.btn:active { transform: scale(.985); }
.btn:disabled { opacity: .45; cursor: default; }
.btn-primary { background: var(--violet); color: #fff; }
.btn-quiet { background: var(--card); color: var(--ink); border-color: var(--line); }
.btn-quiet:hover { border-color: var(--ink-faint); }
.btn-ghost {
  background: none; border: none; min-height: 40px; padding: 0 10px;
  color: var(--ink-soft); font-size: .9rem;
}
.btn-sm { min-height: 40px; padding: 0 16px; font-size: .88rem; border-radius: var(--r-sm); }

.tag {
  font-family: var(--mono); font-size: .68rem; letter-spacing: .06em;
  padding: 3px 8px; border-radius: 5px;
  background: var(--line-soft); color: var(--ink-soft);
}

.empty {
  display: grid; gap: 10px; justify-items: center; text-align: center;
  padding: 56px 24px; color: var(--ink-soft);
}
.empty .num { font-size: 2rem; color: var(--ink-faint); }

/* ── Retention strip — the app's signature: one bar per question ──────── */
.strip {
  display: flex; align-items: flex-end; gap: 2px;
  height: 40px;
  border-bottom: 1px solid var(--line);
}
.strip i {
  /* max-width keeps a small bank from stretching into fat slabs */
  flex: 1 1 0; min-width: 2px; max-width: 13px;
  border-radius: 2px 2px 0 0;
  background: var(--s-new);
  transform-origin: bottom;
  animation: grow .5s var(--ease) backwards;
}
.strip i[data-s="new"]       { height: 26%; background: var(--s-new); }
.strip i[data-s="learning"]  { height: 52%; background: var(--s-learning); }
.strip i[data-s="review"]    { height: 76%; background: var(--s-review); }
.strip i[data-s="mastered"]  { height: 100%; background: var(--s-mastered); }
.strip i[data-m="1"] { background: var(--ember); }
@keyframes grow { from { transform: scaleY(.06); opacity: 0; } }

.legend { display: flex; flex-wrap: wrap; gap: 4px 16px; }
.legend span {
  display: flex; align-items: center; gap: 6px;
  font-family: var(--mono); font-size: .7rem; color: var(--ink-soft);
}
.legend b { width: 8px; height: 8px; border-radius: 2px; }

/* ── Dashboard ───────────────────────────────────────────────────────── */
.hero { display: grid; gap: 6px; margin-bottom: 26px; }
.hero-num {
  display: flex; align-items: baseline; gap: 12px;
  font-size: clamp(3.4rem, 17vw, 4.6rem); line-height: 1;
}
.hero-num small { font-family: var(--sans); font-size: 1rem; font-weight: 400; color: var(--ink-soft); }

.topics { display: grid; gap: 12px; grid-template-columns: 1fr 1fr; }
.topic {
  display: grid; gap: 8px; text-align: left;
  padding: 16px; cursor: pointer;
  background: var(--card); border: 1px solid var(--line); border-radius: var(--r-md);
  transition: border-color .18s, transform .12s var(--ease);
}
.topic:hover { border-color: var(--violet); }
.topic:active { transform: scale(.99); }
.topic .num { font-size: 1.9rem; }
.topic-name { font-size: .92rem; font-weight: 500; }
.topic-meta {
  display: grid; gap: 1px;
  font-family: var(--mono); font-size: .7rem; color: var(--ink-faint);
}

.streak {
  display: flex; align-items: center; gap: 10px;
  font-family: var(--mono); font-size: .78rem; color: var(--ink-soft);
}
.streak-dots { display: flex; gap: 3px; }
.streak-dots i { width: 6px; height: 6px; border-radius: 50%; background: var(--line); }
.streak-dots i.on { background: var(--violet); }

/* ── Practice ────────────────────────────────────────────────────────── */
.sessionbar {
  position: sticky; top: 0; z-index: 10;
  display: flex; align-items: center; gap: 14px;
  padding: 14px 20px calc(14px + env(safe-area-inset-top));
  background: var(--paper);
}
.progress { flex: 1; height: 3px; background: var(--line); border-radius: 2px; overflow: hidden; }
.progress i { display: block; height: 100%; background: var(--violet); transition: width .35s var(--ease); }
.sessionbar .mono { font-size: .74rem; color: var(--ink-faint); }

.qwrap { padding: 4px 20px 0; animation: rise .32s var(--ease); }
@keyframes rise { from { opacity: 0; transform: translateY(10px); } }

.qhead { display: flex; flex-wrap: wrap; gap: 8px; margin-bottom: 16px; }
.qtext { font-size: 1.16rem; line-height: 1.65; margin-bottom: 22px; }
.qtext code, .prose code {
  font-family: var(--mono); font-size: .87em;
  background: var(--line-soft); padding: 1px 5px; border-radius: 4px;
}
.qtext pre, .prose pre {
  font-family: var(--mono); font-size: .82rem; line-height: 1.55;
  background: var(--line-soft); padding: 12px 14px; border-radius: var(--r-sm);
  overflow-x: auto;
}
.prose { line-height: 1.75; }
.prose p { margin: 0 0 .8em; }
.prose ul, .prose ol { margin: 0 0 .8em; padding-left: 1.3em; }
.prose li { margin-bottom: .3em; }
.prose strong { font-weight: 600; }
.prose > :last-child { margin-bottom: 0; }

.options { display: grid; gap: 10px; }
.opt {
  display: flex; align-items: flex-start; gap: 12px; width: 100%;
  min-height: var(--tap); padding: 14px 16px; text-align: left;
  background: var(--card); border: 1.5px solid var(--line);
  border-radius: var(--r-md); cursor: pointer;
  font-size: 1rem; line-height: 1.5;
  transition: border-color .18s, background .18s, transform .12s var(--ease);
}
.opt:hover:not(:disabled) { border-color: var(--violet); }
.opt:active:not(:disabled) { transform: scale(.99); }
.opt:disabled { cursor: default; }
.opt-key {
  flex: none; display: grid; place-items: center;
  width: 24px; height: 24px; border-radius: 6px;
  background: var(--line-soft); color: var(--ink-soft);
  font-family: var(--mono); font-size: .76rem; font-weight: 500;
}
.opt[data-v="right"] { border-color: var(--jade); background: var(--jade-soft); }
.opt[data-v="right"] .opt-key { background: var(--jade); color: #fff; }
.opt[data-v="wrong"] { border-color: var(--ember); background: var(--ember-soft); }
.opt[data-v="wrong"] .opt-key { background: var(--ember); color: #fff; }
.opt[data-v="dim"] { opacity: .5; }

.verdict {
  display: flex; align-items: center; gap: 8px;
  font-weight: 600; font-size: .95rem; margin-bottom: 8px;
}
.verdict[data-v="right"] { color: var(--jade); }
.verdict[data-v="wrong"] { color: var(--ember); }

.reveal { animation: rise .28s var(--ease); }
.answer {
  margin-top: 8px; padding: 18px;
  background: var(--card); border: 1px solid var(--line);
  border-left: 3px solid var(--violet); border-radius: var(--r-md);
}

.actions {
  position: sticky; bottom: 0;
  margin-top: 16px;
  padding: 14px 0 calc(16px + env(safe-area-inset-bottom));
  background: var(--paper);
  box-shadow: 0 -16px 20px -10px var(--paper);
}
.grades { display: grid; grid-template-columns: repeat(4, 1fr); gap: 8px; }
.grade {
  display: grid; gap: 2px; place-items: center;
  min-height: 62px; padding: 8px 4px;
  border: 1.5px solid var(--line); border-radius: var(--r-md);
  background: var(--card); cursor: pointer;
  transition: border-color .18s, transform .12s var(--ease);
}
.grade:active { transform: scale(.97); }
.grade b { font-size: .92rem; font-weight: 500; }
.grade small { font-family: var(--mono); font-size: .66rem; color: var(--ink-faint); }
.grade[data-g="0"]:hover { border-color: var(--ember); }
.grade[data-g="1"]:hover, .grade[data-g="2"]:hover, .grade[data-g="3"]:hover { border-color: var(--violet); }

.summary { display: grid; gap: 22px; justify-items: center; text-align: center; padding: 40px 0; }
.summary .num { font-size: 3.4rem; }
.summary-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 10px; width: 100%; }
.summary-grid div {
  padding: 14px 8px; border: 1px solid var(--line);
  border-radius: var(--r-md); background: var(--card);
}
.summary-grid b { display: block; font-family: var(--serif); font-size: 1.5rem; }
.summary-grid small { font-size: .72rem; color: var(--ink-faint); }

/* ── Lists (mistakes / browse / weakest) ─────────────────────────────── */
.item {
  display: grid; gap: 10px; width: 100%; text-align: left;
  padding: 16px; background: var(--card);
  border: 1px solid var(--line); border-radius: var(--r-md);
  cursor: pointer; font: inherit;
  transition: border-color .18s;
}
.item:hover { border-color: var(--ink-faint); }
.item-q { font-size: .96rem; line-height: 1.55; }
.item-meta { display: flex; flex-wrap: wrap; align-items: center; gap: 8px 12px; }

.dots { display: flex; gap: 4px; align-items: center; }
.dots i { width: 7px; height: 7px; border-radius: 50%; border: 1.5px solid var(--ember); }
.dots i.on { background: var(--ember); }

.state-pill {
  font-family: var(--mono); font-size: .66rem; letter-spacing: .04em;
  padding: 2px 7px; border-radius: 4px; color: #fff;
}
.state-pill[data-s="new"]      { background: var(--s-new); color: var(--ink-soft); }
.state-pill[data-s="learning"] { background: var(--s-learning); }
.state-pill[data-s="review"]   { background: var(--s-review); }
.state-pill[data-s="mastered"] { background: var(--s-mastered); }

.filters { display: flex; flex-wrap: wrap; gap: 6px; margin-bottom: 16px; }
.chip {
  padding: 7px 14px; border-radius: 999px;
  border: 1px solid var(--line); background: var(--card);
  font-size: .85rem; color: var(--ink-soft); cursor: pointer;
  transition: border-color .18s, color .18s;
}
.chip[aria-pressed="true"] { background: var(--ink); border-color: var(--ink); color: var(--paper); }

.search {
  width: 100%; min-height: 46px; padding: 0 16px;
  border: 1px solid var(--line); border-radius: var(--r-md);
  background: var(--card); margin-bottom: 12px;
}
.search::placeholder { color: var(--ink-faint); }

/* ── Stats ───────────────────────────────────────────────────────────── */
.statgrid { display: grid; grid-template-columns: repeat(2, 1fr); gap: 12px; }
.stat { padding: 16px; background: var(--card); border: 1px solid var(--line); border-radius: var(--r-md); }
.stat .num { font-size: 2rem; display: block; }
.stat .eyebrow { margin-bottom: 2px; }
.scroll-x { overflow-x: auto; padding-bottom: 6px; }
.chart-note { font-family: var(--mono); font-size: .68rem; color: var(--ink-faint); }

.bars { display: grid; gap: 24px; }
.bar-track { height: 8px; border-radius: 4px; background: var(--line); overflow: hidden; }
.bar-track i { display: block; height: 100%; border-radius: 4px; background: var(--s-mastered); }

/* ── Login ───────────────────────────────────────────────────────────── */
.login {
  min-height: 100dvh; display: grid; align-content: center; gap: 26px;
  max-width: 380px; margin: 0 auto; padding: 32px 24px;
}
.login-mark { display: flex; align-items: flex-end; gap: 3px; height: 40px; margin-bottom: 4px; }
.login-mark i { width: 9px; border-radius: 3px; background: var(--s-new); animation: grow .6s var(--ease) backwards; }
.login form { display: grid; gap: 10px; }
.field { display: grid; gap: 6px; }
.field input {
  min-height: var(--tap); padding: 0 16px;
  border: 1px solid var(--line); border-radius: var(--r-md);
  background: var(--card);
}
.field input:focus { border-color: var(--violet); }
.error { color: var(--ember); font-size: .86rem; min-height: 1.2em; }

/* ── Desktop ─────────────────────────────────────────────────────────── */
@media (min-width: 720px) {
  .railnav { display: flex; }
  .tabbar { display: none; }
  .view { padding-bottom: 60px; }
  .topics { grid-template-columns: 1fr 1fr; }
  .statgrid { grid-template-columns: repeat(4, 1fr); }
  .qwrap, .sessionbar { padding-left: 0; padding-right: 0; }
  body.focusmode .view { padding-left: 24px; padding-right: 24px; }
}

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { animation-duration: .001ms !important; transition-duration: .001ms !important; }
}