:root {
  --blue: #3d9ac2;
  --light-blue: #e6f7ff;
  --paper: #f8f9fa;
  --ink: #303030;
  --muted: #65717a;
  --line: #d9e1e6;
}

* { box-sizing: border-box; }
body { margin: 0; color: var(--ink); background: white; font-family: Verdana, Geneva, sans-serif; line-height: 1.65; }
a { color: var(--blue); }
.site-header { min-height: 76px; padding: 0 5vw; display: flex; align-items: center; justify-content: space-between; background: var(--light-blue); border-bottom: 1px solid var(--line); }
.brand { display: flex; align-items: center; gap: 12px; color: var(--ink); text-decoration: none; font-size: .75rem; line-height: 1.25; letter-spacing: .04em; }
.brand strong { font-size: .95rem; }
.brand-logo { display: block; width: auto; max-width: 150px; max-height: 44px; object-fit: contain; }
.brand-mark { display: grid; place-items: center; width: 40px; height: 40px; border: 2px solid var(--blue); color: var(--blue); font-weight: bold; }
.layout { display: grid; grid-template-columns: 280px minmax(0, 900px); gap: 5vw; max-width: 1440px; margin: auto; padding: 48px 5vw 80px; }
.layout--overview { display: block; max-width: 1040px; }
.sidebar { position: sticky; top: 24px; align-self: start; max-height: calc(100vh - 48px); overflow: auto; }
.lesson-nav { display: grid; gap: 3px; }
.lesson-link { padding: 9px 12px; color: var(--muted); text-decoration: none; border-left: 3px solid transparent; font-size: .85rem; line-height: 1.35; }
.lesson-link:hover, .lesson-link.is-active { color: var(--ink); border-left-color: var(--blue); background: var(--light-blue); }
.content { min-width: 0; }
.hero { padding: 40px 0 50px; max-width: 720px; }
.hero h1, .content > h1 { margin: 0 0 18px; color: var(--ink); font-family: "Proxima Nova", Verdana, sans-serif; font-size: clamp(2.2rem, 5vw, 4.4rem); line-height: 1.05; letter-spacing: -.04em; }
.hero p:not(.eyebrow) { max-width: 610px; color: var(--muted); font-size: 1.1rem; }
.eyebrow { color: var(--blue); font-size: .72rem; font-weight: bold; letter-spacing: .14em; text-transform: uppercase; }
.lesson-list { border-top: 1px solid var(--line); }
.lesson-row { display: grid; grid-template-columns: 54px 1fr 30px; align-items: center; gap: 16px; padding: 18px 10px; color: var(--ink); border-bottom: 1px solid var(--line); text-decoration: none; }
.lesson-row:hover { background: var(--light-blue); }
.lesson-row > span:first-child { color: var(--blue); font-size: .75rem; font-weight: bold; }
.lesson-row h2 { margin: 0; font-family: "Proxima Nova", Verdana, sans-serif; font-size: 1.05rem; line-height: 1.3; }
.lesson-arrow { color: var(--blue); font-size: 1.3rem; text-align: right; }
.lesson-content { padding: 26px 0; border-top: 1px solid var(--line); }
.lesson-content img { display: block; max-width: 100%; height: auto; margin: 24px auto; }
.lesson-content pre { overflow-x: auto; padding: 18px; background: var(--light-blue); color: var(--ink); border-left: 4px solid var(--blue); }
.lesson-content pre code { font-family: Consolas, "Courier New", monospace; }
.protected-code { display: contents; }
.protected-code[hidden] { display: none; }
.protected-code pre { margin: 0; }
.lesson-content .code-comment { color: #708090; }
.lesson-content .code-string { color: #a31515; }
.lesson-content .code-preprocessor { color: #795e26; }
.lesson-content .code-number { color: #098658; }
.lesson-content .code-keyword { color: #0000ff; font-weight: 600; }
.lesson-content .code-type { color: #267f99; }
.lesson-content .code-function { color: #795e26; }
.lesson-content .image-frame { margin: 24px 0; }
.lesson-content .image-frame img { margin: 0 auto; }
.lesson-content .c4l-keyconcept,
.lesson-content .c4l-attention {
  min-width: 200px;
  max-width: 75%;
  margin: 48px auto;
  padding: 24px 36px 30px;
  border: 0;
  border-left: 6px solid;
  border-radius: 0;
  position: relative;
}
.lesson-content .c4l-keyconcept {
  background: #f1f5fe;
  border-left-color: #387af1;
}
.lesson-content .c4l-attention {
  padding-right: 48px;
  background: #fef6ed;
  border-left-color: #f88923;
}
.lesson-content .c4l-keyconcept a,
.lesson-content .c4l-attention a {
  overflow-wrap: anywhere;
}
.pager { display: flex; justify-content: space-between; gap: 20px; padding-top: 24px; border-top: 1px solid var(--line); }
.menu-toggle { display: none; padding: 8px 12px; color: var(--ink); background: white; border: 1px solid var(--line); }
@media (max-width: 800px) {
  .layout { display: block; padding-top: 24px; }
  .sidebar { display: none; position: static; max-height: none; margin-bottom: 28px; }
  .sidebar.is-open { display: block; }
  .menu-toggle { display: block; }
  .hero { padding-top: 20px; }
  .lesson-content .c4l-keyconcept,
  .lesson-content .c4l-attention { max-width: 100%; }
}