:root {
  --green: #58cc02;
  --green-dark: #46a302;
  --blue: #1cb0f6;
  --red: #ff4b4b;
  --gray: #e5e5e5;
  --text: #3c3c3c;
  --text-soft: #777;
  --bg: #ffffff;
  --panel: #f7f7f7;
  --radius: 16px;
  color-scheme: light dark;
}

* { box-sizing: border-box; }

body {
  margin: 0;
  font-family: -apple-system, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  background: var(--bg);
  color: var(--text);
  position: relative;
}

body::before {
  content: "";
  position: fixed;
  inset: 0;
  z-index: -1;
  background:
    radial-gradient(circle at 15% 20%, rgba(88, 204, 2, 0.16), transparent 40%),
    radial-gradient(circle at 85% 12%, rgba(28, 176, 246, 0.14), transparent 42%),
    radial-gradient(circle at 50% 92%, rgba(255, 200, 0, 0.12), transparent 45%);
}

/* ---------- Liquid glass ---------- */

.glass {
  background: rgba(255, 255, 255, 0.72);
  backdrop-filter: blur(20px) saturate(180%);
  -webkit-backdrop-filter: blur(20px) saturate(180%);
  border: 1px solid rgba(255, 255, 255, 0.55);
  box-shadow: 0 8px 32px rgba(31, 38, 135, 0.10), inset 0 1px 0 rgba(255, 255, 255, 0.6);
}

/* ---------- Icons ---------- */

.icon { display: inline-flex; align-items: center; justify-content: center; }
.icon svg { width: 1em; height: 1em; display: block; }

.topbar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 14px 24px;
  position: sticky;
  top: 0;
  z-index: 10;
  border-radius: 0 0 18px 18px;
}

.brand-group {
  display: flex;
  align-items: center;
}

.brand {
  position: relative;
  font-weight: 800;
  font-size: 20px;
  color: var(--green-dark);
  letter-spacing: 0.5px;
}

.brand-badge {
  position: absolute;
  top: -3px;
  left: 100%;
  margin-left: 7px;
  white-space: nowrap;
  font-size: 9px;
  font-weight: 700;
  letter-spacing: 0.6px;
  text-transform: uppercase;
  padding: 2px 6px;
  border-radius: 4px;
  background: none;
  border: 1px solid var(--gray);
  color: var(--text-soft);
}

.stats { display: flex; align-items: center; gap: 16px; font-size: 14px; }
.stat { display: inline-flex; align-items: center; gap: 6px; font-weight: 600; color: var(--text-soft); position: relative; transition: transform 0.15s ease; }
.stat:not(:last-child)::after {
  content: "";
  position: absolute;
  right: -8px;
  width: 1px;
  height: 14px;
  background: var(--gray);
}
.stat b { font-weight: 700; color: var(--text); font-size: 15px; line-height: 1; }
.stat.bump { animation: bump 0.35s ease; }
.stat-xp .icon, .stat-streak .icon { line-height: 1; }
.stat-xp .icon { color: #b8860b; font-size: 15px; }
.stat-streak .icon { color: #c9622f; font-size: 15px; }

#app {
  max-width: 640px;
  margin: 0 auto;
  padding: 24px 16px 80px;
}

/* ---------- Home / course select ---------- */

.filter-tabs {
  display: flex;
  gap: 8px;
  margin-bottom: 20px;
  flex-wrap: nowrap;
  overflow-x: auto;
  padding-bottom: 6px;
  scrollbar-width: none;
  -ms-overflow-style: none;
}

.filter-tabs::-webkit-scrollbar {
  display: none;
}

.filter-tab {
  flex: 0 0 auto;
  padding: 8px 18px;
  border-radius: 20px;
  border: 2px solid var(--gray);
  background: var(--panel);
  font-family: inherit;
  font-weight: 700;
  font-size: 13px;
  letter-spacing: 0.3px;
  color: var(--text-soft);
  cursor: pointer;
  transition: transform 0.12s ease, background 0.12s ease, border-color 0.12s ease, color 0.12s ease;
}
.filter-tab:hover { border-color: var(--blue); color: var(--text); }
.filter-tab:active { transform: scale(0.96); }
.filter-tab.active {
  background: var(--green);
  border-color: var(--green-dark);
  color: #fff;
}

@media (min-width: 700px) {
  .filter-tabs {
    flex-wrap: wrap;
    overflow-x: visible;
    padding-bottom: 0;
  }
}

.course-list {
  display: flex;
  flex-direction: column;
  gap: 16px;
}

.course-card {
  display: block;
  width: 100%;
  text-align: left;
  border-radius: var(--radius);
  padding: 18px 20px;
  cursor: pointer;
  font-family: inherit;
  transition: transform 0.15s ease, border-color 0.15s ease, box-shadow 0.15s ease;
  animation: fadeInUp 0.35s ease both;
}
.course-list .course-card:nth-child(1) { animation-delay: 0.02s; }
.course-list .course-card:nth-child(2) { animation-delay: 0.08s; }
.course-list .course-card:nth-child(3) { animation-delay: 0.14s; }
.course-list .course-card:nth-child(n+4) { animation-delay: 0.18s; }

.course-card:hover { border-color: var(--blue); transform: translateY(-3px); box-shadow: 0 12px 28px rgba(28, 176, 246, 0.16); }
.course-card:active { transform: translateY(-1px) scale(0.99); }

.course-card-top {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 10px;
}

.course-code {
  font-size: 13px;
  font-weight: 700;
  color: var(--blue);
  text-transform: uppercase;
  letter-spacing: 0.5px;
}

.course-soon-badge {
  display: none;
  font-size: 10px;
  font-weight: 700;
  letter-spacing: 0.4px;
  text-transform: uppercase;
  color: var(--text-soft);
  border: 1px solid var(--gray);
  border-radius: 4px;
  padding: 3px 7px;
  white-space: nowrap;
}

.course-title {
  font-size: 18px;
  font-weight: 700;
  margin-top: 4px;
  color: var(--text);
}

.course-card.empty {
  cursor: not-allowed;
  filter: grayscale(0.6);
  opacity: 0.6;
  animation: none;
}
.course-card.empty:hover { transform: none; box-shadow: none; border-color: var(--gray); }
.course-card.empty .course-soon-badge { display: inline-block; }
.course-card.empty .course-code,
.course-card.empty .course-title { color: var(--text-soft); }

.course-progress {
  margin-top: 12px;
  height: 8px;
  background: var(--gray);
  border-radius: 4px;
  overflow: hidden;
}

.course-progress-bar {
  height: 100%;
  background: var(--green);
  width: 0%;
  transition: width 0.3s;
}

/* ---------- Chapter path ---------- */

.back-btn {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  background: none;
  border: none;
  color: var(--text-soft);
  font-size: 15px;
  cursor: pointer;
  margin-bottom: 12px;
  padding: 4px 0;
  transition: color 0.15s ease, transform 0.15s ease;
}
.back-btn .icon svg { width: 15px; height: 15px; }
.back-btn:hover { color: var(--text); transform: translateX(-2px); }

.course-heading {
  margin-bottom: 24px;
}
.course-heading h1 { margin: 0 0 4px; font-size: 22px; }
.course-heading p { margin: 0; color: var(--text-soft); }
.course-heading .course-note {
  margin-top: 8px;
  font-size: 13px;
  font-style: italic;
  color: var(--blue);
}

.path {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 28px;
  padding: 10px 0 30px;
}

.node-wrap { display: flex; width: 100%; animation: fadeInUp 0.4s ease both; }
.node-wrap:nth-child(1) { animation-delay: 0.02s; }
.node-wrap:nth-child(2) { animation-delay: 0.07s; }
.node-wrap:nth-child(3) { animation-delay: 0.12s; }
.node-wrap:nth-child(4) { animation-delay: 0.17s; }
.node-wrap:nth-child(5) { animation-delay: 0.22s; }
.node-wrap:nth-child(n+6) { animation-delay: 0.26s; }
.node-wrap.pos-0 { justify-content: center; }
.node-wrap.pos-1 { justify-content: flex-start; padding-left: 12%; }
.node-wrap.pos-2 { justify-content: flex-end; padding-right: 12%; }
.node-wrap.pos-3 { justify-content: flex-start; padding-left: 24%; }

.chapter-node {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 6px;
  background: none;
  border: none;
  cursor: pointer;
  font-family: inherit;
  width: 90px;
}

.node-circle {
  position: relative;
  width: 68px;
  height: 68px;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 22px;
  font-weight: 800;
  color: #fff;
  background: var(--gray);
  border-bottom: 5px solid #cfcfcf;
  transition: transform 0.15s cubic-bezier(.34,1.56,.64,1);
}

.chapter-node.in-progress .node-circle::after {
  content: "";
  position: absolute;
  top: -2px;
  right: -2px;
  width: 16px;
  height: 16px;
  border-radius: 50%;
  background: var(--blue);
  border: 2.5px solid var(--bg);
}
.node-circle .icon svg { width: 26px; height: 26px; }

.chapter-node:hover .node-circle { transform: scale(1.08); }
.chapter-node:active .node-circle { transform: scale(0.95); }
.chapter-node.completed .node-circle { animation: popIn 0.4s cubic-bezier(.34,1.56,.64,1) both; }

.chapter-node.locked .node-circle { background: var(--gray); border-color: #cfcfcf; color: #aaa; }
.chapter-node.locked { cursor: not-allowed; opacity: 0.7; }
.chapter-node.available .node-circle { background: var(--green); border-color: var(--green-dark); }
.chapter-node.completed .node-circle { background: var(--blue); border-color: #1899d6; }
.chapter-node.empty .node-circle { background: var(--gray); border-color: #cfcfcf; color: #bbb; }
.chapter-node.empty { cursor: not-allowed; opacity: 0.55; }

.node-title {
  font-size: 12px;
  text-align: center;
  color: var(--text-soft);
  font-weight: 600;
  line-height: 1.3;
}

/* ---------- Lesson ---------- */

.progress-track {
  display: flex;
  gap: 6px;
  margin-bottom: 28px;
}
.progress-seg {
  flex: 1;
  height: 12px;
  border-radius: 6px;
  background: var(--gray);
  transition: background 0.25s;
}
.progress-seg.filled { background: var(--green); }
.progress-seg.current { background: var(--blue); }

.card {
  border-radius: var(--radius);
  padding: 26px 24px;
  min-height: 260px;
  display: flex;
  flex-direction: column;
  justify-content: center;
  animation: fadeInUp 0.35s ease both;
}

.card h2 {
  margin: 0 0 14px;
  font-size: 20px;
  color: var(--green-dark);
}

.card p {
  white-space: pre-line;
  line-height: 1.55;
  font-size: 16px;
  margin: 0 0 14px;
  color: var(--text);
}

.card p:last-child { margin-bottom: 0; }

.card strong,
.feedback-box strong {
  color: var(--green-dark);
  font-weight: 800;
}

.card-list,
.feedback-box .card-list {
  margin: 0 0 14px;
  padding-left: 22px;
  line-height: 1.55;
  font-size: 16px;
  color: var(--text);
}

.card-list:last-child { margin-bottom: 0; }

.card-list li { margin-bottom: 8px; }
.card-list li:last-child { margin-bottom: 0; }

ol.card-list { list-style: decimal; }
ul.card-list { list-style: none; padding-left: 0; }
ul.card-list li {
  padding-left: 24px;
  position: relative;
}
ul.card-list li::before {
  content: "";
  position: absolute;
  left: 4px;
  top: 9px;
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: var(--green);
}

/* ---------- Visuals (diagrams + step animations) ---------- */
.visual-block {
  margin-top: 18px;
}

.visual-frame {
  /* Fixed, theme-independent surface: the diagram's own shape colors are a
     fixed light pastel palette (not dark-mode aware), so the frame and all
     label/connector colors inside it must stay fixed too, or dark mode
     produces low-contrast text against light shapes. */
  background: #f7f7f7;
  border: 1px solid #e0e0e0;
  border-radius: 12px;
  padding: 8px;
  overflow-x: auto;
}

.visual-svg {
  display: block;
  width: 100%;
  height: auto;
  min-width: 480px;
}


.visual-caption {
  margin-top: 8px;
  font-size: 13px;
  font-style: italic;
  color: var(--text-soft);
  text-align: center;
}

.visual-anim-controls {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 14px;
  margin-top: 10px;
}

.visual-step-btn {
  border: 1px solid var(--gray);
  background: var(--bg);
  color: var(--text);
  border-radius: 8px;
  padding: 6px 14px;
  font-size: 13px;
  font-weight: 600;
  cursor: pointer;
  transition: background 0.15s ease, opacity 0.15s ease;
}

.visual-step-btn:hover:not(:disabled) {
  background: var(--panel);
}

.visual-step-btn:disabled {
  opacity: 0.35;
  cursor: default;
}

.visual-step-indicator {
  font-size: 12px;
  color: var(--text-soft);
  min-width: 90px;
  text-align: center;
}

/* ---------- Quiz ---------- */

.quiz-question {
  font-size: 19px;
  font-weight: 700;
  margin-bottom: 20px;
  line-height: 1.4;
  color: var(--text);
  animation: fadeInUp 0.3s ease both;
}

.options { display: flex; flex-direction: column; gap: 12px; animation: fadeInUp 0.35s ease both 0.05s; }

.option {
  text-align: left;
  padding: 14px 18px;
  border: 2px solid var(--gray);
  border-radius: 12px;
  background: #fff;
  color: #3c3c3c;
  font-size: 16px;
  cursor: pointer;
  font-family: inherit;
  appearance: none;
  -webkit-appearance: none;
  transition: border-color 0.15s ease, background 0.15s ease, transform 0.1s ease;
}

.option:hover:not(:disabled) { border-color: var(--blue); transform: translateX(2px); }
.option:active:not(:disabled) { transform: scale(0.98); }
.option:disabled { cursor: default; }

.option.correct { border-color: var(--green); background: #d7ffb8; color: #205000; }
.option.incorrect { border-color: var(--red); background: #ffdfe0; color: #8a0018; }

.feedback-box {
  margin-top: 18px;
  padding: 14px 16px;
  border-radius: 12px;
  font-size: 15px;
  line-height: 1.5;
  color: #3c3c3c;
  animation: fadeInUp 0.3s ease both;
}
.feedback-box.correct { background: #d7ffb8; border: 2px solid var(--green); color: #205000; }
.feedback-box.incorrect { background: #ffdfe0; border: 2px solid var(--red); color: #8a0018; }
.feedback-box .fb-title { font-weight: 800; margin-bottom: 4px; }

/* ---------- Term matching ---------- */

.match-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 10px 12px;
  animation: fadeInUp 0.35s ease both 0.05s;
}

.match-col { display: flex; flex-direction: column; gap: 10px; }

.match-item {
  display: flex;
  align-items: center;
  min-height: 60px;
  text-align: left;
  padding: 12px 14px;
  border: 2px solid var(--gray);
  border-radius: 12px;
  background: #fff;
  color: var(--text);
  font-size: 14px;
  line-height: 1.3;
  cursor: pointer;
  font-family: inherit;
  appearance: none;
  transition: border-color 0.15s ease, background 0.15s ease, transform 0.1s ease;
}

.match-item:hover:not(:disabled) { border-color: var(--blue); }
.match-item:active:not(:disabled) { transform: scale(0.97); }
.match-item:disabled { cursor: default; }

.match-item.selected { border-color: var(--blue); background: #e8f6ff; }
.match-item.matched { border-color: var(--green); background: #d7ffb8; color: #205000; opacity: 0.85; }
.match-item.wrong { border-color: var(--red); background: #ffdfe0; color: #8a0018; animation: shake 0.4s ease; }

@keyframes shake {
  0%, 100% { transform: translateX(0); }
  25% { transform: translateX(-4px); }
  75% { transform: translateX(4px); }
}

/* ---------- Review mistakes ---------- */

.review-mistakes-btn {
  display: flex;
  align-items: center;
  gap: 8px;
  margin: 4px 0 20px;
  padding: 10px 18px;
  border: 2px solid var(--red);
  border-radius: 14px;
  background: none;
  color: var(--red);
  font-size: 14px;
  font-weight: 800;
  font-family: inherit;
  cursor: pointer;
  transition: background 0.15s ease, transform 0.1s ease;
}
.review-mistakes-btn:hover { background: #ffdfe0; }
.review-mistakes-btn:active { transform: scale(0.98); }
.review-mistakes-btn .icon { width: 16px; height: 16px; }
.review-count {
  background: var(--red);
  color: #fff;
  border-radius: 999px;
  padding: 1px 8px;
  font-size: 12px;
}

.node-stack { display: flex; flex-direction: column; align-items: center; gap: 6px; }

.practice-node-btn {
  border: 2px solid var(--blue);
  background: none;
  color: var(--blue);
  border-radius: 10px;
  padding: 4px 12px;
  font-size: 12px;
  font-weight: 800;
  font-family: inherit;
  cursor: pointer;
  transition: background 0.15s ease, transform 0.1s ease;
}
.practice-node-btn:hover { background: #e8f6ff; }
.practice-node-btn:active { transform: scale(0.96); }

.practice-streak {
  font-size: 14px;
  font-weight: 700;
  color: var(--text-soft);
  margin-bottom: 16px;
}

.theory-label {
  font-size: 13px;
  font-weight: 700;
  color: var(--blue);
  text-transform: uppercase;
  letter-spacing: 0.4px;
  margin-bottom: 10px;
}

.theory-answer {
  background: #e8f6ff;
  border: 2px solid var(--blue);
  color: #0a4a68;
}

.your-answer {
  background: #f3f0ff;
  border: 2px solid #9b7bff;
  color: #3d2a80;
}

.theory-draft {
  width: 100%;
  min-height: 120px;
  padding: 14px 16px;
  border: 2px solid var(--gray);
  border-radius: 12px;
  font-family: inherit;
  font-size: 15px;
  color: #3c3c3c;
  background: #fff;
  resize: vertical;
  margin-bottom: 18px;
  transition: border-color 0.15s ease, box-shadow 0.15s ease;
  animation: fadeInUp 0.3s ease both;
}
.theory-draft:focus { outline: none; border-color: var(--blue); box-shadow: 0 0 0 3px rgba(28, 176, 246, 0.15); }

.fitb-sentence {
  font-size: 18px;
  line-height: 2.1;
  color: var(--text);
  margin-bottom: 22px;
}

.fitb-input {
  display: inline-block;
  min-width: 140px;
  margin: 0 2px;
  padding: 4px 8px;
  border: none;
  border-bottom: 2.5px solid var(--blue);
  background: transparent;
  font-family: inherit;
  font-size: 18px;
  font-weight: 700;
  color: var(--text);
  text-align: center;
}
.fitb-input:focus { outline: none; border-bottom-color: var(--green); }
.fitb-input:disabled { opacity: 1; }
.fitb-input.correct { border-bottom-color: var(--green); color: var(--green-dark); background: #d7ffb822; }
.fitb-input.incorrect { border-bottom-color: var(--red); color: #c0392b; background: #ffdfe022; text-decoration: line-through; }

.key-points {
  margin: 10px 0 0;
  padding-left: 20px;
}
.key-points li { margin-bottom: 4px; }

/* ---------- Shared bottom bar ---------- */

.bottom-bar {
  max-width: 640px;
  margin: 24px auto 0;
  display: flex;
  justify-content: flex-end;
}

.btn-primary {
  background: var(--green);
  color: #fff;
  border: none;
  border-bottom: 4px solid var(--green-dark);
  border-radius: 14px;
  padding: 14px 32px;
  font-size: 16px;
  font-weight: 800;
  cursor: pointer;
  font-family: inherit;
  letter-spacing: 0.3px;
  transition: transform 0.12s ease, filter 0.12s ease, box-shadow 0.12s ease;
}
.btn-primary:hover:not(:disabled) { filter: brightness(1.05); transform: translateY(-2px); box-shadow: 0 6px 16px rgba(88, 204, 2, 0.3); }
.btn-primary:active:not(:disabled) { transform: translateY(0) scale(0.97); }
.btn-primary:disabled { background: var(--gray); border-color: #cfcfcf; color: #aaa; cursor: not-allowed; }

.btn-secondary {
  background: none;
  color: var(--text-soft);
  border: 2px solid var(--gray);
  border-radius: 14px;
  padding: 12px 28px;
  font-size: 16px;
  font-weight: 800;
  cursor: pointer;
  font-family: inherit;
  letter-spacing: 0.3px;
  transition: transform 0.12s ease, border-color 0.12s ease;
}
.btn-secondary:hover { border-color: var(--text-soft); transform: translateY(-2px); }
.btn-secondary:active { transform: translateY(0) scale(0.97); }

/* ---------- Chapter complete ---------- */

.complete-screen {
  text-align: center;
  padding: 40px 0;
  position: relative;
  overflow: hidden;
}
.complete-badge {
  width: 84px;
  height: 84px;
  border-radius: 50%;
  background: var(--green);
  color: #fff;
  display: flex;
  align-items: center;
  justify-content: center;
  margin: 0 auto 16px;
  box-shadow: 0 8px 24px rgba(88, 204, 2, 0.35);
  animation: popIn 0.5s cubic-bezier(.34,1.56,.64,1) both;
}
.complete-badge .icon svg { width: 42px; height: 42px; }
.complete-screen h1 { margin: 0 0 6px; animation: fadeInUp 0.35s ease both 0.1s; }
.complete-screen p { animation: fadeInUp 0.35s ease both 0.15s; }
.complete-screen .xp-earned { color: var(--green-dark); font-weight: 800; font-size: 18px; margin: 14px 0 30px; animation: fadeInUp 0.35s ease both 0.2s; }

.confetti-container { position: absolute; inset: 0; pointer-events: none; overflow: hidden; }
.confetti-piece {
  position: absolute;
  top: -12px;
  width: 8px;
  height: 14px;
  border-radius: 2px;
  opacity: 0;
  animation-name: confettiFall;
  animation-timing-function: ease-in;
  animation-fill-mode: forwards;
}

/* ---------- Keyframes ---------- */

@keyframes fadeInUp {
  from { opacity: 0; transform: translateY(14px); }
  to { opacity: 1; transform: none; }
}

@keyframes popIn {
  from { opacity: 0; transform: scale(0.8); }
  to { opacity: 1; transform: scale(1); }
}

@keyframes bump {
  0% { transform: scale(1); }
  35% { transform: scale(1.1); }
  100% { transform: scale(1); }
}

@keyframes confettiFall {
  0% { transform: translateY(0) translateX(0) rotate(0deg); opacity: 1; }
  100% { transform: translateY(320px) translateX(var(--drift)) rotate(540deg); opacity: 0; }
}

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.001ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.001ms !important;
  }
}

@media (prefers-color-scheme: dark) {
  :root {
    --text: #eaeaea;
    --text-soft: #a0a0a0;
    --bg: #131313;
    --panel: #1e1e1e;
    --gray: #333;
  }
  body::before {
    background:
      radial-gradient(circle at 15% 20%, rgba(88, 204, 2, 0.14), transparent 40%),
      radial-gradient(circle at 85% 12%, rgba(28, 176, 246, 0.16), transparent 42%),
      radial-gradient(circle at 50% 92%, rgba(255, 200, 0, 0.10), transparent 45%);
  }
  .glass {
    background: rgba(24, 24, 24, 0.62);
    border-color: rgba(255, 255, 255, 0.08);
    box-shadow: 0 8px 32px rgba(0, 0, 0, 0.45), inset 0 1px 0 rgba(255, 255, 255, 0.05);
  }
  .option { background: #1a1a1a; color: var(--text); }
  .match-item { background: #1a1a1a; color: var(--text); }
  .match-item.selected { background: #16324a; }
  .course-card:hover { transform: translateY(-3px); }
}