.site-header, main { width: min(100% - 40px, 960px); margin-inline: auto; }
.site-header { display: flex; align-items: center; justify-content: space-between; padding: 12px 0; font-size: 12px; color: var(--muted); }
.site-header > a { text-decoration: none; }
.lesson-menu { position: relative; }
.lesson-menu summary { cursor: pointer; }
.lesson-menu nav { position: absolute; right: 0; top: 28px; width: 280px; max-width: calc(100vw - 40px); max-height: calc(100vh - 70px); overflow-y: auto; padding: 8px; background: var(--page); border: 1px solid var(--line); border-radius: 4px; box-shadow: 0 4px 14px #25372f14; z-index: 2; }
.lesson-menu nav a { display: block; padding: 8px; text-decoration: none; }
.lesson-menu nav a:hover, .lesson-menu nav a[aria-current] { background: var(--soft); color: var(--green); }
main { padding: 4px 0 30px; outline: none; }
h1 { font-size: 30px; line-height: 1.25; font-weight: 600; letter-spacing: -.8px; margin: 0 0 12px; }
.lesson-toolbar { display: flex; align-items: center; justify-content: space-between; gap: 16px; border-bottom: 1px solid var(--line); margin-bottom: 16px; }
.lesson-tabs { display: flex; gap: 24px; }
.lesson-tabs button { padding: 6px 0 8px; font-size: 13px; background: none; border-bottom: 2px solid transparent; color: var(--muted); margin-bottom: -1px; }
.lesson-tabs button[aria-selected="true"] { border-color: var(--green); color: var(--green); font-weight: 600; }
.source-link { font-size: 12px; color: var(--muted); text-decoration: none; white-space: nowrap; }
.source-link:hover { color: var(--green); text-decoration: underline; }
.attribution { border-top: 1px solid var(--line); font-size: 11px; color: var(--muted); margin-top: 24px; padding-top: 12px; }
.attribution summary { cursor: pointer; }
.attribution p { margin: 8px 0 0; }
.visually-hidden { position: absolute; width: 1px; height: 1px; padding: 0; overflow: hidden; clip-path: inset(50%); white-space: nowrap; border: 0; }
@media (max-width: 600px) {
  .site-header, main { width: calc(100% - 32px); }
  h1 { font-size: 26px; }
  .lesson-tabs { gap: 20px; }
}