/* Free /learn course. Self-contained: no web fonts, no CDN, no images. */
:root {
  --ink: #1d2433; --muted: #5a6478; --line: #d9dee8; --bg: #ffffff; --soft: #f4f6fa;
  --brand: #0b4f8a; --brand-ink: #ffffff; --ok: #1d6b3a; --warn-bg: #fff6e0; --warn-line: #e6c36a;
  --focus: #f0a400;
}
@media (prefers-color-scheme: dark) {
  :root { --ink: #e7eaf1; --muted: #a9b2c3; --line: #343c4d; --bg: #12161f; --soft: #1b212d;
          --brand: #6fb2f0; --brand-ink: #0b1220; --ok: #6fd39a; --warn-bg: #2a2414; --warn-line: #7a6427; }
}
* { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; }
body { margin: 0; background: var(--bg); color: var(--ink);
       font: 18px/1.65 system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif; }
.wrap { max-width: 46rem; margin: 0 auto; padding: 0 1rem; }
a { color: var(--brand); }
a:focus-visible, button:focus-visible, input:focus-visible, summary:focus-visible {
  outline: 3px solid var(--focus); outline-offset: 2px; }
.skip { position: absolute; left: -999px; top: 0; background: var(--bg); padding: .5rem 1rem; }
.skip:focus { left: 1rem; z-index: 10; }
header.site { border-bottom: 1px solid var(--line); }
header.site .wrap { display: flex; justify-content: space-between; align-items: center; gap: 1rem;
                    padding-top: .75rem; padding-bottom: .75rem; }
.brand { font-weight: 700; text-decoration: none; color: var(--ink); }
.course-link { font-size: .9rem; }
.notice { background: var(--warn-bg); border-bottom: 1px solid var(--warn-line); font-size: .9rem; }
.notice .wrap { padding-top: .5rem; padding-bottom: .5rem; }
main.wrap { padding-top: 1.75rem; padding-bottom: 3rem; }
h1 { font-size: 2rem; line-height: 1.2; margin: .25rem 0 .75rem; }
h2 { font-size: 1.35rem; margin-top: 2rem; }
h3 { font-size: 1.1rem; margin-top: 1.5rem; }
.eyebrow { text-transform: uppercase; letter-spacing: .06em; font-size: .8rem; color: var(--muted); margin: 0; }
.lead { font-size: 1.15rem; }
.meta, .crumbs { color: var(--muted); font-size: .9rem; }
.button { display: inline-block; background: var(--brand); color: var(--brand-ink); border: 0;
          border-radius: .4rem; padding: .6rem 1.1rem; font: inherit; font-weight: 600;
          text-decoration: none; cursor: pointer; }
button.link { background: none; border: 0; padding: 0; color: var(--brand); font: inherit;
              text-decoration: underline; cursor: pointer; }
.lessons { padding-left: 1.25rem; }
.lessons li { margin: 0 0 1rem; }
.lessons li a { font-weight: 600; }
.lessons p { margin: .2rem 0 0; color: var(--muted); }
.minutes { color: var(--muted); font-size: .85rem; margin-left: .4rem; }
.done { color: var(--ok); font-size: .85rem; font-weight: 600; margin-left: .4rem; }
.done::before { content: "\2713 "; }
.lesson blockquote, .callout { background: var(--soft); border-left: 4px solid var(--brand);
                               margin: 1.25rem 0; padding: .75rem 1rem; }
.lesson table { border-collapse: collapse; width: 100%; font-size: .95rem; margin: 1rem 0; }
.lesson th, .lesson td { border: 1px solid var(--line); padding: .45rem .6rem; text-align: left; vertical-align: top; }
.lesson th { background: var(--soft); }
.pager { display: flex; justify-content: space-between; align-items: center; gap: 1rem; flex-wrap: wrap;
         border-top: 1px solid var(--line); margin-top: 2.5rem; padding-top: 1.25rem; }
.questions { padding-left: 1.25rem; }
.question { margin-bottom: 1.5rem; }
.question fieldset { border: 1px solid var(--line); border-radius: .4rem; padding: .75rem 1rem; margin: 0; }
.question legend { font-weight: 600; padding: 0 .25rem; }
.question label { display: block; padding: .25rem 0; cursor: pointer; }
.question.correct fieldset { border-color: var(--ok); }
.question.incorrect fieldset { border-color: #c0392b; }
.explain { margin-top: .5rem; }
.result { font-weight: 600; }
footer.site { border-top: 1px solid var(--line); color: var(--muted); font-size: .85rem; padding: 1rem 0 2rem; }
code { font-size: .85em; }
@media (max-width: 30rem) { body { font-size: 17px; } h1 { font-size: 1.6rem; } }