:root {
  --font-body: "Georgia", "Times New Roman", serif;
  --font-sans: "Segoe UI", system-ui, -apple-system, sans-serif;
  --font-mono: "SFMono-Regular", Consolas, "Liberation Mono", monospace;
  --ink: #142133;
  --muted: #4a5568;
  --accent: #155956;
  --surface: #ffffff;
  --surface-alt: #f6f7fb;
  --border: #d8dde6;
  --shadow: 0 10px 30px rgba(12, 24, 39, 0.08);
}

* {
  box-sizing: border-box;
}

body {
  font-family: var(--font-body);
  color: var(--ink);
  background: #eef1f5;
  line-height: 1.65;
  font-size: 17px;
  margin: 0;
}

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

h1, h2, h3, h4, h5, h6 {
  font-family: var(--font-sans);
  font-weight: 700;
  line-height: 1.2;
  color: #0f1626;
  margin-top: 1.2em;
  margin-bottom: 0.4em;
}
h1 { font-size: 2rem; }
h2 { font-size: 1.6rem; }
h3 { font-size: 1.3rem; }

p {
  margin: 0 0 0.9em;
  color: var(--muted);
}

ul, ol {
  color: var(--muted);
  padding-left: 1.2rem;
}

code, pre {
  font-family: var(--font-mono);
  background: #f2f4f8;
  border-radius: 6px;
}

code {
  padding: 0.1rem 0.3rem;
}

pre {
  padding: 0.9rem 1rem;
  overflow-x: auto;
  border: 1px solid var(--border);
  color: #1c1f23;
}

blockquote {
  margin: 1rem 0;
  padding: 0.75rem 1rem;
  border-left: 4px solid var(--accent);
  background: var(--surface-alt);
  color: var(--muted);
}

table {
  border-collapse: collapse;
  width: 100%;
  margin: 1rem 0;
  background: var(--surface);
  box-shadow: var(--shadow);
}

th, td {
  padding: 0.55rem 0.75rem;
  border: 1px solid var(--border);
  text-align: left;
}

th {
  background: #eef3f9;
  font-family: var(--font-sans);
  font-weight: 700;
}

.page-content .wrapper {
  background: var(--surface);
  padding: 1.5rem 1.8rem;
  border: 1px solid var(--border);
  border-radius: 12px;
  box-shadow: var(--shadow);
  max-width: 1080px;
  margin: 1.4rem auto;
}

.site-footer {
  text-align: center;
  color: var(--muted);
  margin: 2rem 0;
  font-size: 0.95rem;
}

.sidebar {
  background: var(--surface);
  border-color: var(--border);
  box-shadow: var(--shadow);
}

.sidebar__header {
  font-family: var(--font-sans);
}

.lecture-nav__list a.active {
  background: var(--accent);
  color: #fff;
}

.lecture-nav__list a:hover,
.lecture-nav__list a:focus-visible {
  background: #e0f2ef;
  color: #0b362f;
}

img {
  max-width: 100%;
  height: auto;
  border-radius: 8px;
}

.hero,
.panel {
  box-shadow: var(--shadow);
}

@media (max-width: 720px) {
  body {
    font-size: 16px;
  }
  .page-content .wrapper {
    padding: 1.1rem 1.25rem;
    margin: 1rem auto;
  }
}