/* Bài 1 */
body {
  font-family: Arial, sans-serif;
  line-height: 1.65;
  color: #203047;
  max-width: 68rem;
  margin: 0 auto;
  padding: 1rem;
}

/* Bài 2 */
.intro { font-size: 1.125rem; color: #425a73; }
.card h3 { color: #173957; }
.card a { text-decoration-thickness: 0.12em; }
.site-nav > a { color: #125a82; }

/* Bài 3 */
.notice { color: #1d4ed8; }
.notice.is-important { color: #9f1239; }
/* Dòng sau vẫn không thắng selector có hai class ở trên. */
.notice { color: #166534; }

/* Bài 4 */
*, *::before, *::after { box-sizing: border-box; }
.sample-box {
  width: 240px;
  max-width: 100%;
  padding: 20px;
  border: 4px solid #247c9c;
  margin-block: 1rem;
  background: #e9f5fb;
}

/* Bài 5 */
.measure-box {
  width: min(100%, 32rem);
  padding: 1rem;
  border: 1px solid #a8bfd1;
  margin-block: 1rem;
}
.measure-box p { margin-block: 0 1em; }

/* Bài 6 */
.reading, .type-sample { max-width: 65ch; }
.type-sample { font-size: 1.125rem; line-height: 1.75; }
.type-sample h3 { line-height: 1.25; margin-block: 1.5em 0.5em; }
button, input, select, textarea { font: inherit; }

/* Bài 7 */
.hero { background: #e9f4ff; border: 1px solid #b8d6ee; border-radius: 1rem; padding: 1.5rem; }
.eyebrow { color: #145b7c; font-size: .85rem; font-weight: 700; letter-spacing: .08em; }
.card { border: 1px solid #cbd8e5; border-radius: .75rem; padding: 1rem; background: #fff; }
.color-sample { padding: 1rem; color: #123c54; background: #dff2f1; border-left: .35rem solid #19746e; }

/* Bài 8 */
.button { display: inline-block; padding: .55rem .9rem; color: #fff; background: #175f82; border-radius: .4rem; text-decoration: none; }
.overflow-sample { max-width: 100%; width: 26rem; border: 1px solid #b9cad9; padding: .8rem; }
.overflow-sample code { overflow-wrap: anywhere; }
.scroll-code { max-width: 100%; overflow-x: auto; }

/* Bài 9 */
img { max-width: 100%; height: auto; }
.card img { display: block; width: 100%; aspect-ratio: 16 / 9; object-fit: cover; border-radius: .5rem; }
.image-sample { max-width: 32rem; margin: 0; }
.image-sample img { display: block; width: 100%; height: auto; }
.image-sample figcaption { color: #425a73; font-size: .9rem; }

/* Bài 10 */
.position-card { position: relative; border: 1px solid #acc4d7; padding: 3rem 1rem 1rem; max-width: 30rem; }
.badge { position: absolute; top: .6rem; right: .6rem; background: #173957; color: #fff; padding: .15rem .6rem; border-radius: 1rem; }
.sticky-demo { height: 10rem; overflow: auto; border: 1px solid #acc4d7; margin-block: 1rem; }
.sticky-demo h3 { position: sticky; top: 0; margin: 0; padding: .4rem; background: #e9f4ff; z-index: 1; }
.sticky-demo p { padding-inline: .7rem; }

/* Bài 11 */
.flex-sample { display: flex; align-items: center; justify-content: space-between; gap: .75rem; padding: 1rem; border: 1px solid #b8cada; }
.flex-sample span { padding: .5rem; background: #e9f4ff; }
@media (max-width: 28rem) { .flex-sample { flex-direction: column; align-items: stretch; } }

/* Bài 12 */
.site-header { display: flex; align-items: center; justify-content: space-between; flex-wrap: wrap; gap: 1rem; padding-block: 1rem; border-bottom: 1px solid #cbd8e5; }
.brand { font-size: 1.35rem; font-weight: 700; color: #173957; text-decoration: none; }
.site-nav { display: flex; align-items: center; flex-wrap: wrap; gap: .5rem; }
.site-nav a { padding: .45rem .65rem; border-radius: .35rem; text-decoration: none; }
.action-row { display: flex; flex-wrap: wrap; gap: .75rem; margin-block: 1rem; }

/* Bài 13 */
.cards { display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); gap: 1rem; }
.cards > * { min-width: 0; }
@media (max-width: 42rem) { .cards { grid-template-columns: 1fr; } }