/* 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; } }

/* Bài 14 */
.cards { grid-template-columns: repeat(auto-fit, minmax(min(100%, 16rem), 1fr)); }
.content-layout { display: grid; grid-template-columns: minmax(0, 1fr); gap: 1rem; margin-block: 1rem; }
.content-layout > * { min-width: 0; padding: 1rem; background: #edf5fb; }
@media (min-width: 48rem) { .content-layout { grid-template-columns: minmax(0, 2fr) minmax(12rem, 1fr); } }

/* Bài 15 */
.responsive-sample { display: grid; grid-template-columns: 1fr; gap: 1rem; }
.responsive-sample > section { padding: 1rem; background: #e9f4ff; border-radius: .5rem; }
@media (min-width: 42rem) { .responsive-sample { grid-template-columns: repeat(2, minmax(0, 1fr)); } }
.hero h1 { font-size: clamp(1.7rem, 1.2rem + 2vw, 2.8rem); line-height: 1.15; }

/* Bài 16 */
@media (max-width: 34rem) {
  .site-header { align-items: stretch; }
  .site-nav { width: 100%; }
  .site-nav a { flex: 1 1 auto; text-align: center; }
}
.table-region { max-width: 100%; overflow-x: auto; margin-block: 1rem; }
.table-region table { min-width: 36rem; border-collapse: collapse; }
.table-region th, .table-region td { border: 1px solid #b8cada; padding: .6rem; text-align: left; }
.long-content { overflow-wrap: anywhere; }
.table-region:focus-visible { outline: 3px solid #175f82; outline-offset: 3px; }

/* Bài 17 */
.contact-form { max-width: 36rem; }
.contact-form label { display: block; font-weight: 700; margin-top: 1rem; }
.contact-form input, .contact-form textarea { width: 100%; padding: .65rem; border: 1px solid #839db4; border-radius: .4rem; font: inherit; }
.contact-form button { padding: .6rem 1rem; margin: 1rem .5rem 0 0; border: 1px solid #175f82; border-radius: .4rem; background: #175f82; color: #fff; }
a:focus-visible, button:focus-visible, input:focus-visible, textarea:focus-visible { outline: 3px solid #b25b00; outline-offset: 3px; }
@media (hover: hover) { .button:hover, .contact-form button:not(:disabled):hover { background: #104761; } }
.contact-form button:disabled { opacity: .65; cursor: not-allowed; }
.help, .form-note { font-size: .9rem; color: #425a73; }
.error-message { color: #9f1239; font-weight: 700; }

/* Bài 18 */
:root { --color-accent: #175f82; --color-ink: #203047; --color-border: #cbd8e5; --radius: .65rem; --space: 1rem; }
body { color: var(--color-ink); }
.button, .contact-form button { background: var(--color-accent); }
.card { border-color: var(--color-border); border-radius: var(--radius); }
.theme-sample { padding: var(--space); border: 2px solid var(--color-accent); border-radius: var(--radius); }
.theme-sample strong { color: var(--color-accent); }

/* Bài 19 */
.motion-card { padding: 1rem; border: 1px solid #a8bfd1; border-radius: .6rem; transition: transform 160ms ease, box-shadow 160ms ease; }
@media (hover: hover) { .motion-card:hover { transform: translateY(-3px); box-shadow: 0 8px 20px #1739571a; } }
.motion-card:focus-within { box-shadow: 0 0 0 3px #b25b0055; }
@media (prefers-reduced-motion: reduce) { .motion-card { transition: none; } .motion-card:hover { transform: none; } }

/* Bài 20 */
.site-footer { margin-top: 2rem; padding-block: 1rem; border-top: 1px solid var(--color-border, #cbd8e5); color: #425a73; }
.skip-link { display: inline-block; margin-block: .4rem; }
.review-panel { border: 1px solid #8bb7a6; background: #edf8f2; padding: 1rem; border-radius: .6rem; }
.review-panel ul { padding-inline-start: 1.3rem; }