:root {
  --bg: #f3f6f3;
  --bg-start: #e9efe9;
  --panel: #ffffff;
  --text: #122117;
  --muted: #5f6f62;
  --ok: #1d8f42;
  --ok-soft: #e7f8eb;
  --bad: #c3362a;
  --bad-soft: #ffe9e6;
  --line: #dce6dc;
  --focus: #3a8f62;
  --input-bg: #ffffff;
  --input-border: #b7c9b9;
  --button-bg: #f7fbf8;
  --card-bg: #ffffff;
  --toast-bg: #122117;
  --toast-text: #ffffff;
  --danger-border: #dab8b5;
  --danger-text: #8a2f27;
  --danger-bg: #fff7f6;
  --keycap-bg: #f8fbf9;
  --keycap-border: #cedbce;
  --feedback-known-bg: #dff2e4;
  --feedback-known-text: #1a723b;
  --feedback-unknown-bg: #ffe7e4;
  --feedback-unknown-text: #a33228;
  --progress-track: #e2ebe3;
  --progress-fill-a: #68ba7f;
  --progress-fill-b: #2b9850;
  --shadow-known: #66b67f;
  --shadow-unknown: #d77b72;
}

html[data-theme="dark"] {
  --bg: #11161a;
  --bg-start: #1d252b;
  --panel: #1b2329;
  --text: #e4edf2;
  --muted: #a4b2bb;
  --ok: #4abf7a;
  --ok-soft: #1f3a2a;
  --bad: #e27167;
  --bad-soft: #3b2525;
  --line: #33414a;
  --focus: #6bbd92;
  --input-bg: #1f2a31;
  --input-border: #41525d;
  --button-bg: #233039;
  --card-bg: #202931;
  --toast-bg: #ecf4f8;
  --toast-text: #0f1b22;
  --danger-border: #7f504c;
  --danger-text: #f2b9b3;
  --danger-bg: #3a2a2a;
  --keycap-bg: #1f2a31;
  --keycap-border: #4e606d;
  --feedback-known-bg: #2d5138;
  --feedback-known-text: #8de3af;
  --feedback-unknown-bg: #5b3030;
  --feedback-unknown-text: #f5b9b3;
  --progress-track: #2d3a42;
  --progress-fill-a: #4fae74;
  --progress-fill-b: #2f8d54;
  --shadow-known: #4fae74;
  --shadow-unknown: #d17870;
}

h1,
h2,
h3 {
  margin: 0 0 8px;
  line-height: 1.25;
  letter-spacing: 0.01em;
}

h1 {
  font-size: 28px;
  font-weight: 700;
}

h2 {
  font-size: 22px;
  font-weight: 700;
}

p {
  line-height: 1.45;
}

@media (prefers-color-scheme: dark) {
  html[data-theme="system"] {
    --bg: #11161a;
    --bg-start: #1d252b;
    --panel: #1b2329;
    --text: #e4edf2;
    --muted: #a4b2bb;
    --ok: #4abf7a;
    --ok-soft: #1f3a2a;
    --bad: #e27167;
    --bad-soft: #3b2525;
    --line: #33414a;
    --focus: #6bbd92;
    --input-bg: #1f2a31;
    --input-border: #41525d;
    --button-bg: #233039;
    --card-bg: #202931;
    --toast-bg: #ecf4f8;
    --toast-text: #0f1b22;
    --danger-border: #7f504c;
    --danger-text: #f2b9b3;
    --danger-bg: #3a2a2a;
    --keycap-bg: #1f2a31;
    --keycap-border: #4e606d;
    --feedback-known-bg: #2d5138;
    --feedback-known-text: #8de3af;
    --feedback-unknown-bg: #5b3030;
    --feedback-unknown-text: #f5b9b3;
    --progress-track: #2d3a42;
    --progress-fill-a: #4fae74;
    --progress-fill-b: #2f8d54;
    --shadow-known: #4fae74;
    --shadow-unknown: #d17870;
  }
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: "Trebuchet MS", "Segoe UI", sans-serif;
  color: var(--text);
  background: radial-gradient(circle at 0% 0%, var(--bg-start) 0, var(--bg) 45%);
}

.container {
  width: min(980px, 92vw);
  margin: 0 auto;
}

.topbar {
  padding: 18px 0;
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
}

.brand {
  color: var(--text);
  text-decoration: none;
  font-size: 24px;
  font-weight: 700;
}

.panel {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 14px;
  padding: 16px;
  margin: 12px 0;
}

.stack {
  display: grid;
  gap: 8px;
}

input,
button,
select {
  border-radius: 10px;
  border: 1px solid var(--input-border);
  background: var(--input-bg);
  color: var(--text);
  padding: 10px 12px;
  font-size: 16px;
  font: inherit;
}

input:focus-visible,
button:focus-visible,
select:focus-visible,
a:focus-visible {
  outline: 2px solid var(--focus);
  outline-offset: 2px;
}

button {
  cursor: pointer;
  background: var(--button-bg);
  transition: background-color 0.15s ease, border-color 0.15s ease, transform 0.08s ease;
}

button:hover {
  filter: brightness(0.98);
}

button:active {
  transform: translateY(1px);
}

button:disabled {
  cursor: not-allowed;
  opacity: 0.6;
}

.muted {
  color: var(--muted);
}

.quickbar {
  position: sticky;
  top: 8px;
  z-index: 10;
  backdrop-filter: blur(4px);
}

.quickbar-head {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 12px;
}

.quickbar-head h1 {
  margin: 0;
  font-size: clamp(24px, 3.2vw, 28px);
}

.sort-select {
  min-width: 190px;
}

.collection-list,
.card-list {
  list-style: none;
  padding: 0;
  margin: 0;
  display: grid;
  gap: 8px;
}

.collection-list li,
.card-list li {
  border: 1px solid var(--line);
  border-radius: 10px;
  padding: 12px;
  display: grid;
  gap: 6px;
}

.collection-item {
  gap: 8px;
}

.collection-item-head {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 12px;
}

.collection-title {
  color: var(--text);
  text-decoration: none;
  font-weight: 700;
  font-size: 20px;
  line-height: 1.3;
  overflow-wrap: anywhere;
}

.collection-meta {
  display: flex;
  gap: 14px;
  flex-wrap: wrap;
}

.metric-label {
  font-size: 13px;
  color: var(--muted);
  line-height: 1.4;
}

.collection-actions {
  display: flex;
  align-items: center;
  gap: 10px;
}

.secondary-link {
  color: var(--muted);
  text-decoration: none;
}

.secondary-link:hover {
  text-decoration: underline;
}

.badge {
  display: inline-flex;
  align-items: center;
  border: 1px solid var(--line);
  border-radius: 999px;
  padding: 4px 10px;
  color: var(--muted);
  font-size: 14px;
  white-space: nowrap;
}

.continue-card {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 12px;
}

.continue-title {
  margin: 0;
  font-size: 20px;
  font-weight: 700;
}

.success-link {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  border: 1px solid var(--line);
  border-radius: 10px;
  padding: 10px 16px;
  text-decoration: none;
  background: var(--ok-soft);
  color: var(--text);
  font-weight: 700;
}

.hidden {
  display: none;
}

.study-topline {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 12px;
}

.study-topline h1 {
  margin: 0;
  font-size: 24px;
}

.study-wrap {
  margin-top: 20px;
  perspective: 1000px;
}

.flashcard {
  width: 100%;
  min-height: 280px;
  cursor: pointer;
  position: relative;
}

.flashcard-inner {
  position: relative;
  width: 100%;
  min-height: 280px;
  text-align: center;
  transform-style: preserve-3d;
  transition: transform 0.45s;
}

.flashcard.is-flipped .flashcard-inner {
  transform: rotateY(180deg);
}

.flashcard-face {
  position: absolute;
  inset: 0;
  border: 1px solid var(--line);
  border-radius: 16px;
  background: var(--card-bg);
  padding: 20px;
  backface-visibility: hidden;
  display: grid;
  place-content: center;
  gap: 12px;
}

.flashcard-face h2 {
  font-size: clamp(30px, 5vw, 42px);
  line-height: 1.2;
  margin: 0;
}

.flashcard-back {
  transform: rotateY(180deg);
}

.flashcard.feedback-known .flashcard-face {
  box-shadow: 0 0 0 2px var(--shadow-known) inset;
}

.flashcard.feedback-unknown .flashcard-face {
  box-shadow: 0 0 0 2px var(--shadow-unknown) inset;
}

.answer-feedback {
  position: absolute;
  top: 12px;
  right: 12px;
  z-index: 3;
  border-radius: 999px;
  padding: 6px 10px;
  font-size: 13px;
  font-weight: 700;
  opacity: 0;
  transform: translateY(-4px);
  animation: fade-in-out 0.55s ease forwards;
}

.answer-feedback.is-known {
  background: var(--feedback-known-bg);
  color: var(--feedback-known-text);
}

.answer-feedback.is-unknown {
  background: var(--feedback-unknown-bg);
  color: var(--feedback-unknown-text);
}

@keyframes fade-in-out {
  0% {
    opacity: 0;
    transform: translateY(-4px);
  }
  20% {
    opacity: 1;
    transform: translateY(0);
  }
  100% {
    opacity: 0;
    transform: translateY(-2px);
  }
}

.answer-row {
  margin-top: 16px;
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 10px;
}

.progress-row {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 10px;
  margin-top: 8px;
  font-size: 14px;
  line-height: 1.4;
}

.progress-track {
  margin-top: 8px;
  height: 10px;
  border-radius: 999px;
  background: var(--progress-track);
  overflow: hidden;
}

.progress-fill {
  height: 100%;
  background: linear-gradient(90deg, var(--progress-fill-a) 0%, var(--progress-fill-b) 100%);
}

.danger {
  background: var(--bad-soft);
  border-color: #e8b8b2;
}

.success {
  background: var(--ok-soft);
  border-color: #abd9b8;
}

.ghost {
  margin-top: 10px;
  background: transparent;
}

.danger-link {
  color: var(--danger-text);
  border-color: var(--danger-border);
  background: var(--danger-bg);
}

.secondary {
  width: fit-content;
  margin: 0 auto;
}

.button-link {
  display: inline-block;
  margin-top: 8px;
}

.keycap {
  display: inline-flex;
  min-width: 22px;
  justify-content: center;
  border: 1px solid var(--keycap-border);
  border-radius: 6px;
  font-size: 12px;
  padding: 1px 4px;
  background: var(--keycap-bg);
}

.card-row {
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  gap: 12px;
}

.card-row-main {
  display: grid;
  gap: 4px;
}

.toast {
  position: fixed;
  right: 18px;
  bottom: 18px;
  z-index: 50;
  background: var(--toast-bg);
  color: var(--toast-text);
  border-radius: 10px;
  padding: 10px 12px;
  font-size: 14px;
  opacity: 0;
  transform: translateY(6px);
  transition: opacity 0.2s ease, transform 0.2s ease;
}

.topbar-right {
  display: flex;
  align-items: center;
  gap: 12px;
}

.theme-control {
  display: inline-flex;
  align-items: center;
  gap: 8px;
}

.theme-control select {
  min-width: 140px;
  padding: 6px 8px;
  font-size: 14px;
}

.toast.is-visible {
  opacity: 1;
  transform: translateY(0);
}

@media (max-width: 640px) {
  h1 {
    font-size: 22px;
  }

  h2 {
    font-size: 18px;
  }

  .brand {
    font-size: 20px;
  }

  .topbar {
    align-items: flex-start;
    flex-direction: column;
    gap: 4px;
  }

  .topbar-right {
    width: 100%;
    justify-content: space-between;
  }

  .quickbar {
    top: 4px;
  }

  .quickbar-head {
    flex-direction: column;
    align-items: stretch;
  }

  .collection-item-head {
    align-items: flex-start;
    flex-direction: column;
  }

  .collection-actions {
    width: 100%;
    justify-content: space-between;
  }

  .continue-card {
    flex-direction: column;
    align-items: flex-start;
  }

  .card-row {
    flex-direction: column;
    align-items: stretch;
  }

  .flashcard,
  .flashcard-inner {
    min-height: 240px;
  }

  body[data-page="study"] .topbar {
    padding: 10px 0 6px;
  }

  body[data-page="study"] .topbar .muted {
    display: none;
  }

  body[data-page="study"] .study-panel {
    padding: 10px 12px;
    margin: 8px 0;
  }

  body[data-page="study"] .study-topline h1 {
    font-size: 18px;
  }

  body[data-page="study"] .progress-row {
    margin-top: 4px;
    font-size: 13px;
  }

  body[data-page="study"] .progress-track {
    margin-top: 6px;
    height: 6px;
  }

  body[data-page="study"] .study-summary {
    display: none;
  }

  body[data-page="study"] .study-wrap {
    margin-top: 8px;
  }

  .collection-title {
    font-size: 18px;
  }

  .flashcard-face h2 {
    font-size: clamp(26px, 8vw, 34px);
  }

  .answer-row {
    position: sticky;
    bottom: max(8px, env(safe-area-inset-bottom));
    background: var(--bg);
    padding: 8px 0;
  }

  .toast {
    left: 12px;
    right: 12px;
    bottom: max(12px, env(safe-area-inset-bottom));
  }
}