/* Đa Thức — nhiều biến số cho tư duy đầu tư. Thẩm mỹ: giấy cũ, đọc lâu không mỏi mắt. */

@import url('https://fonts.googleapis.com/css2?family=Source+Serif+4:ital,opsz,wght@0,8..60,400;0,8..60,500;0,8..60,600;0,8..60,700;1,8..60,400&family=Inter:wght@400;500;600&display=swap');

:root {
  --bg: #FAF6EF;
  --bg-raised: #F2EBDD;
  --ink: #262220;
  --ink-soft: #5B5450;
  --rule: #DDD2BE;
  --accent: #2F5D50;
  --accent-soft: #E4ECE8;
  --link: #2F5D50;
  --code-bg: #EFE7D6;

  --serif: "Source Serif 4", Georgia, "Times New Roman", serif;
  --sans: "Inter", -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;

  color-scheme: light;
}

html[data-theme="dark"] {
  --bg: #17161A;
  --bg-raised: #201F24;
  --ink: #E9E4D8;
  --ink-soft: #A79E8F;
  --rule: #35333A;
  --accent: #7FB69A;
  --accent-soft: #23302B;
  --link: #7FB69A;
  --code-bg: #211F26;
  color-scheme: dark;
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font-family: var(--serif);
  font-size: 17px;
  line-height: 1.7;
  -webkit-font-smoothing: antialiased;
  transition: background .2s ease, color .2s ease;
}

.site-header {
  position: sticky;
  top: 0;
  z-index: 10;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 16px 24px;
  background: color-mix(in srgb, var(--bg) 88%, transparent);
  backdrop-filter: blur(8px);
  border-bottom: 1px solid var(--rule);
  font-family: var(--sans);
}

.site-header .brand {
  display: flex;
  align-items: baseline;
  gap: 10px;
  text-decoration: none;
  color: var(--ink);
}

.site-header .brand .mark {
  font-family: var(--serif);
  font-weight: 700;
  font-size: 20px;
  letter-spacing: 0.02em;
}

.site-header .brand .tagline {
  font-size: 12px;
  color: var(--ink-soft);
  letter-spacing: 0.03em;
}

.theme-toggle {
  appearance: none;
  border: 1px solid var(--rule);
  background: var(--bg-raised);
  color: var(--ink);
  font-family: var(--sans);
  font-size: 13px;
  font-weight: 500;
  padding: 7px 12px;
  border-radius: 999px;
  cursor: pointer;
  display: flex;
  align-items: center;
  gap: 6px;
  transition: background .15s ease, transform .1s ease;
}
.theme-toggle:hover { background: var(--accent-soft); }
.theme-toggle:active { transform: scale(0.97); }
.theme-toggle:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }

main {
  max-width: 720px;
  margin: 0 auto;
  padding: 48px 24px 120px;
}

.eyebrow {
  font-family: var(--sans);
  font-size: 12px;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--accent);
  font-weight: 600;
  margin-bottom: 10px;
}

h1 {
  font-family: var(--serif);
  font-weight: 700;
  font-size: clamp(28px, 5vw, 40px);
  line-height: 1.15;
  margin: 0 0 8px;
  letter-spacing: -0.01em;
}

h2 {
  font-family: var(--serif);
  font-weight: 600;
  font-size: 26px;
  margin: 2.4em 0 0.7em;
  padding-top: 0.6em;
  border-top: 1px solid var(--rule);
}
main > h2:first-of-type { border-top: none; padding-top: 0; }

h3 {
  font-family: var(--serif);
  font-weight: 600;
  font-size: 19px;
  color: var(--ink);
  margin: 1.8em 0 0.5em;
}

p { margin: 0 0 1.1em; color: var(--ink); }
em { color: var(--ink-soft); font-style: italic; }

a { color: var(--link); text-decoration-color: color-mix(in srgb, var(--link) 40%, transparent); text-underline-offset: 3px; }
a:hover { text-decoration-thickness: 2px; }

hr { border: none; border-top: 1px solid var(--rule); margin: 2.5em 0; }

.meta {
  font-family: var(--sans);
  font-size: 13px;
  color: var(--ink-soft);
  margin: 0 0 2em;
}

/* Table of contents */
#mục-lục + ul, nav.toc ul {
  list-style: none;
  padding: 0;
  margin: 0;
  font-family: var(--sans);
  font-size: 14.5px;
  background: var(--bg-raised);
  border: 1px solid var(--rule);
  border-radius: 10px;
  padding: 8px 20px;
}
#mục-lục + ul li, nav.toc li { padding: 7px 0; border-bottom: 1px dashed var(--rule); }
#mục-lục + ul li:last-child, nav.toc li:last-child { border-bottom: none; }
#mục-lục + ul ul { margin-top: 4px; margin-left: 6px; border: none; padding: 0 0 0 14px; background: none; }
#mục-lục + ul ul li { border-bottom: none; padding: 3px 0; color: var(--ink-soft); font-size: 13.5px; }

blockquote {
  margin: 1.5em 0;
  padding: 4px 20px;
  border-left: 3px solid var(--accent);
  color: var(--ink-soft);
  background: var(--accent-soft);
  border-radius: 0 8px 8px 0;
}

strong { font-weight: 600; }

table {
  width: 100%;
  border-collapse: collapse;
  font-family: var(--sans);
  font-size: 14px;
  margin: 1.5em 0;
}
th, td { text-align: left; padding: 8px 12px; border-bottom: 1px solid var(--rule); vertical-align: top; }
th { font-weight: 600; color: var(--ink-soft); font-size: 12.5px; text-transform: uppercase; letter-spacing: .04em; }

code { font-family: ui-monospace, "SF Mono", Menlo, monospace; background: var(--code-bg); padding: 2px 6px; border-radius: 4px; font-size: 0.9em; }

.back-link {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  font-family: var(--sans);
  font-size: 13px;
  color: var(--ink-soft);
  text-decoration: none;
  margin-bottom: 28px;
}
.back-link:hover { color: var(--accent); }

/* Archive index list */
.archive-group { margin-bottom: 40px; }
.archive-group h2 { border-top: none; padding-top: 0; margin-top: 0; }
.archive-list { list-style: none; margin: 0; padding: 0; }
.archive-item {
  display: block;
  padding: 16px 0;
  border-bottom: 1px solid var(--rule);
  text-decoration: none;
  color: var(--ink);
}
.archive-item:hover .archive-title { color: var(--accent); }
.archive-title {
  font-family: var(--serif);
  font-size: 18px;
  font-weight: 600;
  display: block;
  margin-bottom: 4px;
  transition: color .15s ease;
}
.archive-desc { font-family: var(--sans); font-size: 13.5px; color: var(--ink-soft); line-height: 1.5; }
.archive-date { font-family: var(--sans); font-size: 12px; color: var(--ink-soft); float: right; }

.empty-note {
  font-family: var(--sans);
  font-size: 14px;
  color: var(--ink-soft);
  font-style: italic;
}

@media (max-width: 600px) {
  main { padding: 32px 18px 100px; }
  .site-header { padding: 14px 16px; }
  h1 { font-size: 28px; }
  h2 { font-size: 22px; }
}