/* ── Reset & tokens ─────────────────────────────────────── */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

:root {
  --bg:   #0a0a0a;
  --sur:  #111111;
  --sur2: #181818;
  --bdr:  #2a2a2a;
  --txt:  #efefef;
  --mut:  #7a7a7a;
  --sub:  #b0b0b0;
}

/* Light mode token overrides */
body.light {
  --bg:   #f2f2f2;
  --sur:  #ffffff;
  --sur2: #e8e8e8;
  --bdr:  #d0d0d0;
  --txt:  #111111;
  --mut:  #777777;
  --sub:  #444444;
}

/* ── Base ───────────────────────────────────────────────── */
body {
  font-family: system-ui, sans-serif;
  background: var(--bg);
  color: var(--txt);
  min-height: 100vh;
}

.app {
  max-width: 1280px;
  margin: 0 auto;
  padding: 0 32px;
  display: flex;
  flex-direction: column;
  min-height: 100vh;
}

/* ── Header ─────────────────────────────────────────────── */
header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 20px 0 16px;
  border-bottom: 1px solid var(--bdr);
}

.header-right {
  display: flex;
  align-items: center;
  gap: 16px;
}

.logo {
  font-size: 13px;
  letter-spacing: .1em;
  text-transform: uppercase;
  color: var(--mut);
}

.stats {
  display: flex;
  gap: 20px;
}

.stat {
  text-align: right;
}

.stat b {
  display: block;
  font-size: 18px;
  font-weight: 500;
}

.stat small {
  font-size: 11px;
  text-transform: uppercase;
  letter-spacing: .06em;
  color: var(--mut);
}

/* ── Filter bar ─────────────────────────────────────────── */
.filters {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
  align-items: center;
  padding: 14px 0;
  border-bottom: 1px solid var(--bdr);
}

/* Search wrapper */
.search-wrap {
  position: relative;
  flex: 1;
  min-width: 160px;
}

.search-wrap svg {
  position: absolute;
  left: 9px;
  top: 50%;
  transform: translateY(-50%);
  color: var(--mut);
  pointer-events: none;
}

input[type="search"] {
  width: 100%;
  background: var(--sur);
  border: 1px solid var(--bdr);
  color: var(--txt);
  font-size: 13px;
  padding: 7px 10px 7px 30px;
  border-radius: 7px;
  outline: none;
}

input[type="search"]:focus  { border-color: var(--sub); }
input[type="search"]::placeholder { color: var(--mut); }

/* Pills (topic filter) */
.pills {
  display: flex;
  gap: 5px;
  flex-wrap: wrap;
}

.pill {
  font-size: 12px;
  padding: 4px 11px;
  border-radius: 20px;
  border: 1px solid var(--bdr);
  background: transparent;
  color: var(--sub);
  cursor: pointer;
  transition: all .12s;
  white-space: nowrap;
}

.pill:hover         { border-color: var(--sub); color: var(--txt); }
.pill.active        { background: var(--txt); color: var(--bg); border-color: var(--txt); }

/* Mode segmented control */
.seg {
  display: flex;
  flex-wrap: wrap;
  border: 1px solid var(--bdr);
  border-radius: 7px;
  overflow: hidden;
}

.seg button {
  font-size: 12px;
  padding: 5px 11px;
  background: transparent;
  border: none;
  color: var(--mut);
  cursor: pointer;
  text-transform: uppercase;
  letter-spacing: .04em;
  transition: background .12s;
}

.seg button.active { background: var(--sur2); color: var(--txt); }

/* ── Custom scrollbar ───────────────────────────────────── */
::-webkit-scrollbar               { width: 4px; height: 4px; }
::-webkit-scrollbar-track         { background: transparent; }
::-webkit-scrollbar-thumb         { background: var(--bdr); border-radius: 4px; }
::-webkit-scrollbar-thumb:hover   { background: var(--mut); }
* { scrollbar-width: thin; scrollbar-color: var(--bdr) transparent; }

/* ── Card area ──────────────────────────────────────────── */
.card-area {
  flex: 1;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 20px;
  padding: 28px 0;
}

/* Progress bar */
.progress-wrap {
  width: 100%;
}

.progress-meta {
  display: flex;
  justify-content: space-between;
  font-size: 12px;
  color: var(--mut);
  margin-bottom: 6px;
}

.progress-bar {
  height: 1.5px;
  background: var(--bdr);
  border-radius: 2px;
}

.progress-fill {
  height: 100%;
  background: var(--txt);
  border-radius: 2px;
  transition: width .3s;
}

/* 3-D flip card */
.scene {
  width: 100%;
  perspective: 1400px;
}

.card {
  width: 100%;
  min-height: 500px;
  position: relative;
  transform-style: preserve-3d;
  transition: transform .5s cubic-bezier(.4, 0, .2, 1);
  cursor: pointer;
}

.card.flipped { transform: rotateY(180deg); }

.face {
  position: absolute;
  inset: 0;
  backface-visibility: hidden;
  border: 1px solid var(--bdr);
  border-radius: 14px;
  overflow: hidden;
}

/* Front face */
.front {
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  text-align: center;
  padding: 44px 52px;
  background: var(--sur);
}

.card-badge {
  font-size: 11px;
  letter-spacing: .12em;
  text-transform: uppercase;
  color: var(--mut);
  margin-bottom: 14px;
}

.card-question {
  font-size: 23px;
  font-weight: 500;
  line-height: 1.45;
  margin-bottom: 12px;
}

.card-subtitle {
  font-size: 15px;
  color: var(--sub);
  line-height: 1.6;
  max-width: 500px;
}

.card-topic-tag {
  position: absolute;
  top: 14px;
  right: 16px;
  font-size: 11px;
  padding: 2px 8px;
  border-radius: 10px;
  border: 1px solid var(--bdr);
  color: var(--mut);
}

/* Back face */
.back {
  transform: rotateY(180deg);
  background: var(--sur2);
  padding: 28px 36px;
  overflow-y: auto;
}

.back-label {
  font-size: 11px;
  letter-spacing: .12em;
  text-transform: uppercase;
  color: var(--mut);
  margin-bottom: 16px;
}

/* Light-mode prose overrides */
.light .prose code         { background: #e8eef6; color: #2d5986; }
.light .prose pre          { background: #eeeeee; }
.light .prose th           { background: #e4e4e4; }
.light .prose blockquote   { color: var(--sub); }

/* ── Prose (rendered markdown) ──────────────────────────── */
.prose {
  font-size: 15px;
  color: var(--sub);
  line-height: 1.75;
}

.prose h3 {
  font-size: 11px;
  letter-spacing: .1em;
  text-transform: uppercase;
  color: var(--mut);
  font-weight: 500;
  margin: 18px 0 8px;
  padding-bottom: 5px;
  border-bottom: 1px solid var(--bdr);
}

.prose h3:first-child { margin-top: 0; }

.prose p              { margin: 0 0 8px; }
.prose ul, .prose ol  { padding-left: 18px; margin: 0 0 8px; }
.prose li             { margin-bottom: 3px; }
.prose strong         { color: var(--txt); font-weight: 500; }
.prose em             { color: var(--sub); }

.prose code {
  font-family: monospace;
  font-size: 13px;
  background: #1c1c1c;
  padding: 1px 5px;
  border-radius: 4px;
  color: #9db8d2;
}

.prose pre {
  background: #141414;
  border: 1px solid var(--bdr);
  border-radius: 8px;
  padding: 12px 16px;
  margin: 10px 0;
  overflow-x: auto;
}

.prose pre code { background: none; padding: 0; }

.prose blockquote {
  border-left: 2px solid var(--bdr);
  padding-left: 14px;
  color: var(--mut);
  margin: 8px 0;
}

.prose table {
  border-collapse: collapse;
  width: 100%;
  margin: 10px 0;
  font-size: 14px;
}

.prose th, .prose td {
  border: 1px solid var(--bdr);
  padding: 6px 10px;
  text-align: left;
}

.prose th {
  color: var(--txt);
  font-weight: 500;
  background: #161616;
}

.prose .katex-display { overflow-x: auto; margin: 14px 0; }

/* ── Controls ───────────────────────────────────────────── */
.controls {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 14px;
}

.icon-btn {
  width: 40px;
  height: 40px;
  border-radius: 9px;
  background: transparent;
  border: 1px solid var(--bdr);
  color: var(--sub);
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  transition: all .12s;
}

.icon-btn:hover  { border-color: var(--sub); color: var(--txt); }
.icon-btn:active { transform: scale(.95); }

/* Theme & fullscreen buttons (live in header) */
.header-icon-btn {
  width: 32px;
  height: 32px;
  border-radius: 8px;
  background: transparent;
  border: 1px solid var(--bdr);
  color: var(--sub);
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  transition: all .12s;
  flex-shrink: 0;
}
.header-icon-btn:hover  { border-color: var(--sub); color: var(--txt); }
.header-icon-btn:active { transform: scale(.95); }

.mark-btns { display: flex; gap: 8px; }

.mark-btn {
  font-size: 12px;
  padding: 6px 15px;
  border-radius: 7px;
  border: 1px solid var(--bdr);
  background: transparent;
  color: var(--sub);
  cursor: pointer;
  transition: all .12s;
  text-transform: uppercase;
  letter-spacing: .04em;
}

.mark-btn.hard:hover  { border-color: #5a2222; color: #a05555; }
.mark-btn.good:hover  { border-color: #225a22; color: #55a055; }
.mark-btn.marked-hard { border-color: #5a2222 !important; background: #180a0a; color: #a05555; }
.mark-btn.marked-good { border-color: #225a22 !important; background: #0a180a; color: #55a055; }

.hint {
  font-size: 12px;
  color: var(--mut);
  text-align: center;
  letter-spacing: .04em;
}

/* ── Footer ─────────────────────────────────────────────── */
footer {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 14px 0;
  border-top: 1px solid var(--bdr);
}

.sub-pills {
  display: flex;
  gap: 5px;
  flex-wrap: wrap;
}

.shuffle-btn {
  font-size: 12px;
  padding: 5px 13px;
  border-radius: 7px;
  border: 1px solid var(--bdr);
  background: transparent;
  color: var(--sub);
  cursor: pointer;
  transition: all .12s;
}

.shuffle-btn:hover { border-color: var(--sub); color: var(--txt); }

/* ── Star rating (difficulty) ───────────────────────────── */
.star-rating {
  position: absolute;
  bottom: 14px;
  left: 16px;
  display: flex;
  align-items: center;
  gap: 2px;
  z-index: 2;
}

.star-label {
  font-size: 11px;
  letter-spacing: .08em;
  text-transform: uppercase;
  color: var(--mut);
  margin-right: 6px;
  user-select: none;
}

.star {
  background: none;
  border: none;
  color: var(--bdr);
  font-size: 19px;
  line-height: 1;
  padding: 0 2px;
  cursor: pointer;
  transition: color .1s, transform .1s;
}

.star.filled       { color: var(--txt) !important; }
.star.hover-active { color: var(--sub) !important; }
.star:active       { transform: scale(1.25); }

/* ── Fullscreen mode ────────────────────────────────────── */
.app:fullscreen,
.app:-webkit-full-screen,
.app:-moz-full-screen {
  max-width: 100%;
  height: 100vh;
  padding: 16px 48px;
  overflow-y: auto;
  box-sizing: border-box;
  /* background and color are set directly by JS to avoid
     Chrome top-layer breaking CSS custom property resolution */
}

.app:fullscreen .card,
.app:-webkit-full-screen .card,
.app:-moz-full-screen .card {
  min-height: 680px;
}