/* Base */
:root {
  --bg: #f4f7ff;
  --panel: #ffffff;
  --text: #142033;
  --muted: #53627a;
  --line: #dce4f2;
  --accent: #2e5bff;
  --accent-2: #15338b;
  --soft: #eef3ff;
  --shadow: 0 12px 28px rgba(14, 31, 70, 0.08);
}

body.dark {
  --bg: #0e1525;
  --panel: #141e33;
  --text: #eef4ff;
  --muted: #a7b4ce;
  --line: #25314b;
  --accent: #7aa4ff;
  --accent-2: #c8d8ff;
  --soft: #0f1b30;
  --shadow: 0 12px 28px rgba(0, 0, 0, 0.28);
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  font-family: Inter, Arial, sans-serif;
  line-height: 1.7;
  color: var(--text);
  background: linear-gradient(180deg, var(--bg), #edf2fb 60%, var(--bg));
}

h1, h2, h3, h4 {
  line-height: 1.25;
  margin-top: 0;
  color: var(--text);
}

p, li { color: var(--text); }
a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }

.hero {
  display: grid;
  grid-template-columns: 1.6fr 1fr;
  gap: 24px;
  padding: 48px clamp(20px, 4vw, 48px);
  background:
    radial-gradient(circle at top right, rgba(46, 91, 255, 0.12), transparent 28%),
    linear-gradient(135deg, #f8fbff, #edf3ff);
  border-bottom: 1px solid var(--line);
}

body.dark .hero {
  background:
    radial-gradient(circle at top right, rgba(122, 164, 255, 0.12), transparent 30%),
    linear-gradient(135deg, #111a2d, #0d1525);
}

.eyebrow {
  text-transform: uppercase;
  letter-spacing: 0.18em;
  font-size: 0.82rem;
  color: var(--accent);
  font-weight: 800;
  margin-bottom: 12px;
}

.hero h1 {
  font-size: clamp(2rem, 4vw, 3.25rem);
  margin-bottom: 16px;
}

.lead {
  font-size: 1.08rem;
  max-width: 60ch;
  color: var(--muted);
}

.hero__card {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 22px;
  padding: 24px;
  box-shadow: var(--shadow);
  align-self: start;
}

.hero__card ul {
  padding-left: 18px;
  margin: 0;
}

.hero__actions {
  display: flex;
  gap: 12px;
  flex-wrap: wrap;
  margin-top: 20px;
}

.btn {
  border: 1px solid var(--accent);
  border-radius: 999px;
  padding: 12px 18px;
  font-weight: 700;
  cursor: pointer;
  background: transparent;
  color: var(--accent);
}

.btn--primary {
  background: var(--accent);
  color: #fff;
  box-shadow: 0 8px 18px rgba(46, 91, 255, 0.24);
}

.btn--ghost {
  border-color: var(--line);
  color: var(--text);
  background: var(--panel);
}

.layout {
  display: grid;
  grid-template-columns: 260px minmax(0, 1fr);
  gap: 24px;
  padding: 24px clamp(20px, 4vw, 48px) 48px;
  max-width: 1440px;
  margin: 0 auto;
}

.sidebar {
  position: sticky;
  top: 16px;
  align-self: start;
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 18px;
  padding: 18px;
  box-shadow: var(--shadow);
}

.sidebar h2 {
  font-size: 1rem;
  margin-bottom: 14px;
}

.sidebar a {
  display: block;
  padding: 9px 10px;
  border-radius: 10px;
  color: var(--text);
}

.sidebar a:hover {
  background: var(--soft);
  text-decoration: none;
}

.content {
  display: grid;
  gap: 20px;
}

.panel {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 22px;
  padding: clamp(18px, 3vw, 28px);
  box-shadow: var(--shadow);
}

.note {
  background: var(--soft);
  border-left: 5px solid var(--accent);
  padding: 14px 16px;
  border-radius: 12px;
}

.grid-two {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 16px;
}

.card {
  background: linear-gradient(180deg, var(--panel), var(--soft));
  border: 1px solid var(--line);
  border-radius: 18px;
  padding: 18px;
}

.formula-block {
  background: #f8fbff;
  border: 1px solid var(--line);
  border-radius: 16px;
  padding: 14px 16px;
  margin: 14px 0;
  overflow-x: auto;
}

body.dark .formula-block {
  background: #101a2c;
}

.worked {
  border: 1px dashed var(--accent);
  border-radius: 18px;
  padding: 16px 18px;
  background: rgba(46, 91, 255, 0.04);
}

.quiz-card {
  background: linear-gradient(180deg, var(--soft), var(--panel));
  border: 1px solid var(--line);
  border-radius: 18px;
  padding: 18px;
}

.answers {
  margin-top: 16px;
  padding: 14px 16px;
  border-radius: 14px;
  background: var(--soft);
  border: 1px solid var(--line);
}

.hidden { display: none; }

.formula-list {
  display: grid;
  gap: 12px;
}

.formula-item {
  border: 1px solid var(--line);
  border-radius: 14px;
  padding: 10px 12px;
  background: var(--soft);
  overflow-x: auto;
}

.footer {
  padding: 18px 24px 40px;
  text-align: center;
  color: var(--muted);
}

mjx-container {
  max-width: 100% !important;
  overflow-x: auto !important;
  overflow-y: hidden !important;
}

@media (max-width: 980px) {
  .hero,
  .layout,
  .grid-two {
    grid-template-columns: 1fr;
  }

  .sidebar {
    position: static;
  }
}

@media (max-width: 640px) {
  body {
    font-size: 15.5px;
  }

  .hero {
    padding: 28px 16px;
  }

  .layout {
    padding: 16px;
  }

  .panel {
    border-radius: 18px;
    padding: 16px;
  }

  .btn {
    width: 100%;
    text-align: center;
  }

  .lead {
    font-size: 1rem;
  }
}