:root {
  --bg: #f7f6f2;
  --surface: #ffffff;
  --ink: #16181d;
  --ink-2: #4a4f5a;
  --ink-3: #7a808c;
  --line: #e4e2db;
  --accent: #0f5c4d;
  --accent-ink: #ffffff;
  --accent-soft: #e3efe9;
  --tag-bg: #efede6;
  --shadow: 0 1px 2px rgba(20, 20, 20, .04), 0 4px 16px rgba(20, 20, 20, .04);
  color-scheme: light;
}
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg: #111315;
    --surface: #181b1f;
    --ink: #eceae4;
    --ink-2: #b4b7bd;
    --ink-3: #868a92;
    --line: #2a2e34;
    --accent: #5cc3a6;
    --accent-ink: #0b1a16;
    --accent-soft: #17302a;
    --tag-bg: #23272d;
    --shadow: none;
    color-scheme: dark;
  }
}

/* language switching */
html[data-lang="vi"] [data-l="en"],
html[data-lang="en"] [data-l="vi"] { display: none !important; }

* { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; }
body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font: 16px/1.6 Inter, system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
}
a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }
.wrap { max-width: 920px; margin: 0 auto; padding: 0 16px; }

/* header */
.site-header { border-bottom: 1px solid var(--line); background: var(--surface); position: sticky; top: 0; z-index: 5; }
.header-inner { display: flex; align-items: center; justify-content: space-between; height: 60px; gap: 12px; }
.brand { display: flex; align-items: center; gap: 10px; font-weight: 700; color: var(--ink); letter-spacing: -.01em; }
.brand:hover { text-decoration: none; }
.brand-mark { width: 22px; height: 22px; border-radius: 6px; background: linear-gradient(135deg, var(--accent) 0 50%, var(--ink) 50% 100%); }
.lang-toggle { display: inline-flex; border: 1px solid var(--line); border-radius: 8px; overflow: hidden; }
.lang-toggle button { border: 0; background: transparent; color: var(--ink-2); font: 600 13px Inter, sans-serif; padding: 6px 12px; cursor: pointer; }
html[data-lang="vi"] [data-set-lang="vi"],
html[data-lang="en"] [data-set-lang="en"] { background: var(--ink); color: var(--bg); }

/* hero */
.hero { padding: 48px 0 24px; }
.hero h1 { font: 700 clamp(30px, 5vw, 44px)/1.1 "Source Serif 4", Georgia, serif; margin: 0 0 12px; letter-spacing: -.02em; }
.lede { font-size: 18px; color: var(--ink-2); margin: 0 0 8px; max-width: 640px; }
.count { color: var(--ink-3); font-size: 14px; margin: 0; }

/* controls */
.controls { position: sticky; top: 60px; z-index: 4; background: var(--bg); padding: 12px 0; }
#q {
  width: 100%; padding: 12px 14px; font: inherit; color: var(--ink);
  background: var(--surface); border: 1px solid var(--line); border-radius: 10px; outline: none;
}
#q:focus { border-color: var(--accent); box-shadow: 0 0 0 3px var(--accent-soft); }
.tag-filter { display: flex; gap: 8px; overflow-x: auto; padding-top: 10px; scrollbar-width: none; }
.tag-filter::-webkit-scrollbar { display: none; }
.chip {
  flex: none; border: 1px solid var(--line); background: var(--surface); color: var(--ink-2);
  font: 500 13px Inter, sans-serif; padding: 6px 12px; border-radius: 999px; cursor: pointer;
}
.chip.active { background: var(--ink); color: var(--bg); border-color: var(--ink); }

/* cards */
.list { display: grid; gap: 14px; padding: 8px 0 48px; }
.card { background: var(--surface); border: 1px solid var(--line); border-radius: 14px; padding: 20px 22px; box-shadow: var(--shadow); }
.card[hidden] { display: none; }
.card-meta { font-size: 13px; color: var(--ink-3); }
.card-title { font: 600 21px/1.3 "Source Serif 4", Georgia, serif; margin: 6px 0 8px; letter-spacing: -.01em; }
.card-title a { color: var(--ink); }
.card-summary { color: var(--ink-2); margin: 0 0 16px; display: -webkit-box; -webkit-line-clamp: 3; -webkit-box-orient: vertical; overflow: hidden; }
.card-foot { display: flex; flex-wrap: wrap; align-items: center; justify-content: space-between; gap: 12px; }
.tags { display: flex; flex-wrap: wrap; gap: 6px; }
.tag { background: var(--tag-bg); color: var(--ink-2); font-size: 12px; font-weight: 500; padding: 3px 9px; border-radius: 6px; }
.card-actions { display: flex; gap: 8px; flex-wrap: wrap; }

.btn {
  display: inline-flex; align-items: center; gap: 8px; background: var(--accent); color: var(--accent-ink);
  font: 600 14px Inter, sans-serif; padding: 9px 14px; border-radius: 9px; border: 1px solid var(--accent); white-space: nowrap;
}
.btn:hover { text-decoration: none; filter: brightness(1.08); }
.btn-ghost { background: transparent; color: var(--ink); border-color: var(--line); }
.btn-lg { padding: 12px 18px; font-size: 15px; }
.empty { text-align: center; color: var(--ink-3); padding: 32px 0 64px; }

/* post */
.crumbs { padding: 28px 0 0; font-size: 14px; }
.post { padding: 12px 0 56px; }
.post-head { border-bottom: 1px solid var(--line); padding-bottom: 24px; margin-bottom: 8px; }
.post-head h1 { font: 700 clamp(26px, 4.5vw, 38px)/1.15 "Source Serif 4", Georgia, serif; margin: 8px 0 14px; letter-spacing: -.02em; }
.post-actions { display: flex; gap: 10px; flex-wrap: wrap; margin-top: 20px; }
.note { font-size: 13px; color: var(--ink-3); margin: 12px 0 0; }
.post-body { max-width: 680px; }
.post-body h2 { font: 600 13px Inter, sans-serif; text-transform: uppercase; letter-spacing: .08em; color: var(--ink-3); margin: 28px 0 8px; }
.post-body p { font-size: 17px; margin: 0; }
.post-body ul { padding-left: 20px; margin: 0; }
.post-body li { margin: 6px 0; font-size: 16px; }

/* perspectives + research ideas */
.perspectives, .research { padding: 8px 0 0; }
.section-h { font: 600 13px Inter, sans-serif; text-transform: uppercase; letter-spacing: .08em; color: var(--ink-3); margin: 36px 0 8px; }
.ai-note { font-size: 13px; color: var(--ink-3); margin: 0 0 14px; max-width: 680px; }
.persp-grid { display: grid; gap: 14px; grid-template-columns: repeat(auto-fit, minmax(260px, 1fr)); }
.persp { background: var(--surface); border: 1px solid var(--line); border-radius: 14px; padding: 18px; box-shadow: var(--shadow); border-top: 3px solid var(--pc); }
.persp-ws { --pc: #1f4fa3; }
.persp-rt { --pc: #c46a12; }
.persp-ac { --pc: #0f5c4d; }
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) .persp-ws { --pc: #6f9be8; }
  :root:not([data-theme="light"]) .persp-rt { --pc: #e8a35a; }
  :root:not([data-theme="light"]) .persp-ac { --pc: #5cc3a6; }
}
.persp-head { display: flex; gap: 10px; align-items: flex-start; margin-bottom: 10px; }
.persp-dot { width: 10px; height: 10px; border-radius: 50%; background: var(--pc); margin-top: 7px; flex: none; }
.persp-head strong { display: block; font-size: 16px; }
.persp-head small { display: block; color: var(--ink-3); font-size: 12px; }
.persp .take { font: 600 16px/1.45 "Source Serif 4", Georgia, serif; margin: 0 0 8px; }
.persp ul { padding-left: 18px; margin: 0; }
.persp li { font-size: 14.5px; margin: 6px 0; color: var(--ink-2); }
.ri-list { list-style: none; padding: 0; margin: 0; display: grid; gap: 14px; counter-reset: ri; }
.ri { background: var(--surface); border: 1px solid var(--line); border-radius: 14px; padding: 18px 20px; counter-increment: ri; }
.ri h3 { font: 600 18px/1.35 "Source Serif 4", Georgia, serif; margin: 8px 0 10px; }
.ri h3::before { content: counter(ri) ". "; color: var(--accent); }
.ri-tags { display: flex; flex-wrap: wrap; gap: 6px; }
.ri-row { display: grid; grid-template-columns: 150px 1fr; gap: 12px; padding: 8px 0; border-top: 1px dashed var(--line); }
.ri-row span { font-size: 12px; font-weight: 600; text-transform: uppercase; letter-spacing: .05em; color: var(--ink-3); padding-top: 2px; }
.ri-row p { margin: 0; font-size: 15px; }
@media (max-width: 560px) { .ri-row { grid-template-columns: 1fr; gap: 2px; } }

/* footer */
.site-footer { border-top: 1px solid var(--line); color: var(--ink-3); font-size: 13px; padding: 20px 0 32px; }
.site-footer p { margin: 4px 0; }

@media (max-width: 560px) {
  .card { padding: 16px; }
  .card-actions { width: 100%; }
  .card-actions .btn { flex: 1; justify-content: center; }
  .hero { padding-top: 32px; }
}