:root {
  --ink: #1c2430;
  --muted: #5c6b7a;
  --paper: #f3efe6;
  --panel: #fffdf8;
  --line: #d7d0c3;
  --accent: #0f6a5a;
  --accent-2: #c45c26;
  --sidebar: #16352f;
  --sidebar-ink: #e7f2ef;
  --shadow: 0 12px 40px rgba(28, 36, 48, 0.08);
  --radius: 18px;
  --font-display: "Literata", Georgia, serif;
  --font-body: "Source Sans 3", system-ui, sans-serif;
}

* { box-sizing: border-box; }
html, body { height: 100%; }
body {
  margin: 0;
  color: var(--ink);
  font-family: var(--font-body);
  background:
    radial-gradient(1200px 600px at 10% -10%, #dfece7 0%, transparent 55%),
    radial-gradient(900px 500px at 100% 0%, #f0e0d2 0%, transparent 50%),
    linear-gradient(180deg, #efe8da, var(--paper));
}

.auth-overlay {
  position: fixed;
  inset: 0;
  z-index: 100;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 16px;
  background: rgba(22, 53, 47, 0.88);
  backdrop-filter: blur(6px);
}
.auth-overlay[hidden],
.shell[hidden],
.page[hidden] {
  display: none !important;
}
.login-card {
  width: 100%;
  max-width: 380px;
  padding: 1.4rem 1.25rem;
  border-radius: 16px;
  background: var(--panel);
  border: 1px solid var(--line);
  box-shadow: var(--shadow);
}
.login-card h2 {
  margin: 0 0 0.4rem;
  font-family: var(--font-display);
}
.login-hint {
  margin: 0 0 1rem;
  color: var(--muted);
  font-size: 0.92rem;
  line-height: 1.4;
}
.login-field {
  display: flex;
  flex-direction: column;
  gap: 0.35rem;
  margin-bottom: 0.85rem;
  font-size: 0.9rem;
  color: var(--muted);
}
.login-field input {
  border: 1px solid var(--line);
  border-radius: 12px;
  padding: 0.75rem;
  font: inherit;
  font-size: 1rem;
  background: #fff;
}
.login-error {
  margin: 0 0 0.75rem;
  color: #9b2c2c;
  font-size: 0.9rem;
}
.login-submit {
  width: 100%;
  border: 0;
  border-radius: 12px;
  padding: 0.75rem 1rem;
  font: inherit;
  font-weight: 700;
  cursor: pointer;
  color: #fff;
  background: var(--accent);
}
.user-row {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 0.5rem;
  font-size: 0.9rem;
}
.logout-btn {
  padding: 0.35rem 0.65rem !important;
  font-size: 0.82rem !important;
  color: var(--sidebar-ink) !important;
  border-color: rgba(255,255,255,0.35) !important;
}

.shell {
  display: grid;
  grid-template-columns: 280px 1fr;
  min-height: 100vh;
}

.sidebar {
  background: linear-gradient(180deg, #1a4038, var(--sidebar));
  color: var(--sidebar-ink);
  padding: 1.15rem;
  display: flex;
  flex-direction: column;
  gap: 0.85rem;
  border-right: 1px solid #0d2420;
  position: sticky;
  top: 0;
  height: 100vh;
}

.brand-mark {
  margin: 0;
  font-family: var(--font-display);
  font-size: 1.55rem;
  font-weight: 700;
}
.brand-sub { margin: 0.25rem 0 0; opacity: 0.8; font-size: 0.88rem; }

.llm-pill {
  display: inline-flex;
  align-self: flex-start;
  padding: 0.35rem 0.7rem;
  border-radius: 999px;
  background: rgba(255,255,255,0.08);
  font-size: 0.82rem;
}
.llm-pill.ok { background: rgba(80, 180, 140, 0.25); }
.llm-pill.bad { background: rgba(200, 80, 60, 0.28); }

.page-nav {
  display: grid;
  gap: 0.35rem;
}
.page-link {
  text-decoration: none;
  color: inherit;
  padding: 0.7rem 0.8rem;
  border-radius: 12px;
  border: 1px solid transparent;
  font-weight: 600;
}
.page-link:hover { background: rgba(255,255,255,0.08); }
.page-link.active {
  background: rgba(255,255,255,0.14);
  border-color: rgba(255,255,255,0.2);
}

.sidebar-label {
  margin: 0.4rem 0 0;
  font-size: 0.72rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  opacity: 0.65;
}

.lesson-nav {
  overflow: auto;
  flex: 1;
  display: flex;
  flex-direction: column;
  gap: 0.3rem;
  padding-right: 0.2rem;
  min-height: 0;
}
.lesson-btn {
  text-align: left;
  border: 0;
  background: transparent;
  color: inherit;
  padding: 0.5rem 0.6rem;
  border-radius: 10px;
  cursor: pointer;
  font: inherit;
}
.lesson-btn:hover, .lesson-btn.active { background: rgba(255,255,255,0.1); }
.lesson-btn small { display: block; opacity: 0.7; }

.stats-card {
  background: rgba(255,255,255,0.06);
  border-radius: 14px;
  padding: 0.75rem;
}
.stats-card h2 { margin: 0 0 0.45rem; font-size: 0.85rem; letter-spacing: 0.04em; text-transform: uppercase; }
.stats-card dl { margin: 0; display: grid; gap: 0.3rem; }
.stats-card div { display: flex; justify-content: space-between; gap: 1rem; }
.stats-card dt { opacity: 0.75; }
.stats-card dd { margin: 0; font-weight: 700; }

.main {
  display: flex;
  flex-direction: column;
  min-width: 0;
  min-height: 100vh;
  padding: 1.15rem 1.35rem 1.4rem;
}

.topbar { margin-bottom: 0.85rem; }
.eyebrow { margin: 0; color: var(--muted); text-transform: uppercase; letter-spacing: 0.08em; font-size: 0.76rem; }
.topbar h1 { margin: 0.2rem 0 0; font-family: var(--font-display); font-size: clamp(1.35rem, 2vw, 1.9rem); }
.page-caption { margin: 0.35rem 0 0; color: var(--muted); }

.page {
  flex: 1;
  min-height: 0;
  display: flex;
  flex-direction: column;
}

.page-grid {
  display: grid;
  grid-template-columns: minmax(0, 1.15fr) minmax(300px, 0.85fr);
  gap: 1rem;
  flex: 1;
  min-height: 0;
}

.practice-grid .practice-left {
  display: flex;
  flex-direction: column;
  gap: 0.85rem;
  min-height: 0;
  overflow: auto;
}

.content-card, .chat-card {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
}

.content-card {
  padding: 1.1rem 1.2rem;
  overflow: auto;
  max-height: calc(100vh - 7.5rem);
}
.practice-left .content-card {
  max-height: none;
}
.problems {
  display: flex;
  flex-direction: column;
  gap: 0.55rem;
  padding: 0.85rem;
}
.submit-card { padding: 0.9rem; }

.theory-doc h2, .theory-doc h3, .progress-doc h2 {
  font-family: var(--font-display);
}
.theory-doc ol { padding-left: 1.2rem; }
.theory-doc .ideas { color: var(--muted); }

.chat-card {
  display: flex;
  flex-direction: column;
  min-height: 480px;
  max-height: calc(100vh - 7.5rem);
  position: sticky;
  top: 1rem;
}
.chat-head {
  padding: 0.75rem 1rem;
  border-bottom: 1px solid var(--line);
  font-weight: 700;
  color: var(--accent);
}

.messages {
  flex: 1;
  overflow: auto;
  padding: 1rem;
  display: flex;
  flex-direction: column;
  gap: 0.7rem;
}
.bubble {
  max-width: 92%;
  padding: 0.7rem 0.85rem;
  border-radius: 14px;
  white-space: pre-wrap;
  line-height: 1.45;
}
.bubble.user { align-self: flex-end; background: #e7f3ef; }
.bubble.assistant {
  align-self: flex-start;
  background: #f6f1e8;
  border: 1px solid var(--line);
}
.bubble.system {
  align-self: center;
  background: transparent;
  color: var(--muted);
  font-size: 0.9rem;
}

.composer {
  display: grid;
  grid-template-columns: 1fr auto;
  gap: 0.5rem;
  padding: 0.75rem;
  border-top: 1px solid var(--line);
}
.composer.grade { grid-template-columns: 1fr; border-top: 0; padding: 0.5rem 0 0; }
.composer textarea, .composer input {
  width: 100%;
  border: 1px solid var(--line);
  border-radius: 12px;
  padding: 0.65rem 0.75rem;
  font: inherit;
  resize: vertical;
  background: #fff;
}
.composer button, .ghost, .problem-btn {
  border: 0;
  border-radius: 12px;
  background: var(--accent);
  color: white;
  padding: 0.65rem 0.95rem;
  font: inherit;
  font-weight: 600;
  cursor: pointer;
}
.ghost {
  background: transparent;
  color: var(--accent);
  border: 1px solid var(--accent);
}
.composer button:disabled, .ghost:disabled { opacity: 0.45; cursor: not-allowed; }

.problem-btn {
  background: #fff;
  color: var(--ink);
  border: 1px solid var(--line);
  text-align: left;
}
.problem-btn.active {
  border-color: var(--accent);
  box-shadow: inset 0 0 0 1px var(--accent);
}
.problem-btn .diff { color: var(--accent-2); font-size: 0.82rem; }
.problem-meta { margin: 0; color: var(--muted); font-size: 0.92rem; flex: 1; }
.practice-toolbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 0.75rem;
  margin-bottom: 0.65rem;
}
.practice-tools {
  display: flex;
  align-items: center;
  gap: 0.45rem;
  flex-shrink: 0;
}
.timer {
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
  padding: 0.4rem 0.65rem;
  border-radius: 999px;
  border: 1px solid var(--line);
  background: #fff;
  font-variant-numeric: tabular-nums;
  font-weight: 700;
  color: var(--ink);
  min-width: 5.5rem;
}
.timer.running { border-color: var(--accent); color: var(--accent); }
.timer-icon { font-size: 0.95rem; line-height: 1; }

.icon-btn {
  width: 2.4rem;
  height: 2.4rem;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  border-radius: 12px;
  border: 1px solid var(--accent);
  background: transparent;
  color: var(--accent);
  cursor: pointer;
  padding: 0;
}
.icon-btn:hover:not(:disabled) { background: #e7f3ef; }
.icon-btn:disabled { opacity: 0.4; cursor: not-allowed; }
.icon-btn.active {
  background: var(--accent);
  color: #fff;
}

.reveal-box {
  margin-bottom: 0.75rem;
  padding: 0.85rem 0.95rem;
  border-radius: 12px;
  border: 1px dashed var(--accent-2);
  background: #fff8f2;
}
.reveal-box h3 {
  margin: 0 0 0.4rem;
  font-family: var(--font-display);
  font-size: 1rem;
  color: var(--accent-2);
}
.reveal-box .answer-line {
  margin: 0 0 0.55rem;
  font-weight: 700;
}
.reveal-box .solution-text {
  margin: 0;
  white-space: pre-wrap;
  line-height: 1.45;
}
.hint-row {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  margin-bottom: 0.55rem;
}
.verdict-correct { color: #0f6a5a; font-weight: 700; }
.verdict-partial { color: #a15c12; font-weight: 700; }
.verdict-incorrect { color: #9b2c2c; font-weight: 700; }

.progress-doc table {
  width: 100%;
  border-collapse: collapse;
  margin-top: 0.75rem;
}
.progress-doc th, .progress-doc td {
  border-bottom: 1px solid var(--line);
  padding: 0.45rem 0.35rem;
  text-align: left;
  font-size: 0.92rem;
}

@media (max-width: 980px) {
  .shell { grid-template-columns: 1fr; }
  .sidebar {
    position: relative;
    height: auto;
    max-height: none;
  }
  .page-grid { grid-template-columns: 1fr; }
  .chat-card {
    position: static;
    max-height: none;
    min-height: 360px;
  }
  .content-card { max-height: none; }
}