:root {
  --bg: #faf9f6;
  --text: #1a1a1a;
  --muted: #5a5a5a;
  --accent: #b45f06;
  --accent-light: #f3e5d8;
  --border: #d4d0c8;
  --code-bg: #f4f2ee;
  --sidebar: #f0ede8;
  --font-body: "Georgia", "Times New Roman", serif;
  --font-mono: "SFMono-Regular", "Menlo", "Consolas", monospace;
}

* {
  box-sizing: border-box;
}

html {
  font-size: 16px;
}

body {
  margin: 0;
  padding: 0;
  background: var(--bg);
  color: var(--text);
  font-family: var(--font-body);
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
}

.container {
  max-width: 760px;
  margin: 0 auto;
  padding: 2.5rem 1.5rem 4rem;
}

header {
  margin-bottom: 2.5rem;
  padding-bottom: 1rem;
  border-bottom: 1px solid var(--border);
}

header h1 {
  font-size: 2.1rem;
  font-weight: 600;
  margin: 0 0 0.4rem;
  letter-spacing: -0.01em;
}

header .subtitle {
  color: var(--muted);
  font-size: 1.05rem;
  margin: 0;
}

h2 {
  font-size: 1.5rem;
  font-weight: 600;
  margin: 2.2rem 0 0.9rem;
  color: var(--text);
}

h3 {
  font-size: 1.2rem;
  font-weight: 600;
  margin: 1.8rem 0 0.6rem;
}

p, li {
  font-size: 1.02rem;
}

a {
  color: var(--accent);
  text-decoration: none;
}

a:hover {
  text-decoration: underline;
}

code {
  font-family: var(--font-mono);
  font-size: 0.88em;
  background: var(--code-bg);
  padding: 0.12em 0.35em;
  border-radius: 3px;
}

pre {
  background: var(--code-bg);
  padding: 1rem 1.2rem;
  border-radius: 6px;
  overflow-x: auto;
  border-left: 3px solid var(--accent);
}

pre code {
  background: transparent;
  padding: 0;
  font-size: 0.85rem;
  line-height: 1.55;
}

table {
  width: 100%;
  border-collapse: collapse;
  margin: 1.2rem 0;
  font-size: 0.95rem;
}

th, td {
  padding: 0.55rem 0.7rem;
  text-align: left;
  border-bottom: 1px solid var(--border);
}

th {
  background: var(--sidebar);
  font-weight: 600;
}

tr:hover {
  background: rgba(0, 0, 0, 0.015);
}

.highlight {
  background: var(--accent-light);
  padding: 1rem 1.2rem;
  border-radius: 6px;
  margin: 1.2rem 0;
}

.callout {
  border-left: 4px solid var(--accent);
  padding: 0.8rem 1.1rem;
  margin: 1.3rem 0;
  background: var(--sidebar);
}

.callout-title {
  font-weight: 600;
  margin-bottom: 0.3rem;
}

.figure {
  margin: 1.5rem 0;
  text-align: center;
}

.figure-caption {
  color: var(--muted);
  font-size: 0.9rem;
  margin-top: 0.4rem;
}

.sidenote {
  float: right;
  clear: right;
  width: 220px;
  margin-right: -250px;
  font-size: 0.85rem;
  color: var(--muted);
  line-height: 1.45;
}

@media (max-width: 1100px) {
  .sidenote {
    float: none;
    width: 100%;
    margin: 1rem 0;
    padding: 0.8rem 1rem;
    background: var(--sidebar);
    border-radius: 6px;
  }
}

.quiz {
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 1.2rem;
  margin: 1.5rem 0;
  background: #fff;
}

.quiz-question {
  font-weight: 600;
  margin-bottom: 0.8rem;
}

.quiz-options label {
  display: block;
  padding: 0.5rem 0.7rem;
  margin: 0.35rem 0;
  border-radius: 5px;
  cursor: pointer;
  border: 1px solid transparent;
}

.quiz-options label:hover {
  background: var(--code-bg);
}

.quiz-options input {
  margin-right: 0.5rem;
}

.feedback {
  margin-top: 0.8rem;
  padding: 0.7rem 0.9rem;
  border-radius: 5px;
  display: none;
}

.feedback.correct {
  background: #e6f4ea;
  color: #1e7e34;
  display: block;
}

.feedback.incorrect {
  background: #fbeaea;
  color: #a61b1b;
  display: block;
}

footer {
  margin-top: 3rem;
  padding-top: 1rem;
  border-top: 1px solid var(--border);
  color: var(--muted);
  font-size: 0.9rem;
}

.nav {
  display: flex;
  justify-content: space-between;
  margin-top: 2rem;
}

.nav a {
  padding: 0.5rem 0.9rem;
  border: 1px solid var(--border);
  border-radius: 5px;
  background: #fff;
}

.lesson-nav {
  display: flex;
  justify-content: space-between;
  max-width: 760px;
  margin: 3rem auto 0;
  padding: 1.5rem 1.5rem 0;
  border-top: 1px solid var(--border);
  font-size: 0.9rem;
}

.lesson-nav a {
  color: var(--accent);
}

.lesson-nav a:hover {
  text-decoration: underline;
}

.math {
  overflow-x: auto;
  padding: 0.3rem 0;
}