/* Giao diện trang nội dung — chép nguyên từ Worker cũ (onthiai.com), tách ra file để CSP không cần inline */
:root { color-scheme: light dark; }
*:focus-visible { outline: 3px solid #2563eb; outline-offset: 2px; border-radius: 4px; }
.skip-link { position: absolute; top: -40px; left: 8px; background: #1e40af; color: #fff; padding: 10px 16px; text-decoration: none; border-radius: 6px; font-weight: 600; z-index: 100; }
.skip-link:focus { top: 8px; }
body { font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", system-ui, sans-serif; max-width: 800px; margin: 0 auto; padding: 24px 20px 80px; color: #111827; line-height: 1.65; background: #fff; font-size: 16px; }
header { padding: 16px 0 20px; border-bottom: 1px solid #d1d5db; margin-bottom: 32px; display: flex; align-items: center; gap: 16px; flex-wrap: wrap; }
header a.brand { font-weight: 800; font-size: 22px; color: #1e40af; text-decoration: none; }
header a.brand:hover, header a.brand:focus-visible { text-decoration: underline; }
header nav.site-nav { display: flex; align-items: center; gap: 4px; flex-wrap: wrap; flex: 1; }
header nav.site-nav a { color: #374151; text-decoration: none; font-weight: 600; font-size: 15px; padding: 6px 12px; border-radius: 6px; white-space: nowrap; }
header nav.site-nav a:hover, header nav.site-nav a:focus-visible { background: #eff6ff; color: #1e40af; text-decoration: none; }
header nav.site-nav a[aria-current="page"] { color: #1e40af; background: #dbeafe; }
header a.cta { background: #1e40af; color: #fff; padding: 10px 18px; border-radius: 8px; text-decoration: none; font-weight: 600; font-size: 15px; margin-left: auto; }
header a.cta:hover, header a.cta:focus-visible { background: #1e3a8a; }
@media (max-width: 560px) {
  header { gap: 10px; }
  header nav.site-nav { order: 3; flex-basis: 100%; gap: 2px; }
  header nav.site-nav a { font-size: 14px; padding: 5px 10px; }
  header a.cta { margin-left: auto; padding: 8px 14px; font-size: 14px; }
}
h1 { font-size: 32px; font-weight: 800; line-height: 1.25; margin: 0 0 16px; color: #111827; }
h2 { font-size: 24px; font-weight: 700; margin-top: 32px; margin-bottom: 12px; color: #111827; }
h3 { font-size: 19px; font-weight: 700; margin-top: 24px; margin-bottom: 10px; color: #111827; }
h4, h5, h6 { font-weight: 700; margin-top: 20px; margin-bottom: 8px; color: #111827; }
p { margin: 0 0 14px; }
ul { padding-left: 22px; margin: 0 0 14px; }
li { margin-bottom: 4px; }
a { color: #1e40af; }
a:hover, a:focus-visible { text-decoration: underline; }
code { background: #f3f4f6; padding: 2px 6px; border-radius: 4px; font-size: 0.9em; color: #111827; }
pre { background: #f3f4f6; padding: 14px; border-radius: 8px; overflow-x: auto; }
pre code { background: none; padding: 0; }
blockquote { border-left: 4px solid #6b7280; padding: 8px 16px; color: #374151; margin: 16px 0; background: #f9fafb; border-radius: 0 6px 6px 0; }
footer { margin-top: 64px; padding-top: 20px; border-top: 1px solid #d1d5db; color: #4b5563; font-size: 14px; text-align: center; }
footer a { color: #1e40af; }