:root {
  --bg: #0d1220;
  --bg-soft: #141b2e;
  --card: #1a2338;
  --card-2: #202c47;
  --line: #2c3a5c;
  --text: #e8edf7;
  --muted: #97a3bd;
  --accent: #5b9dff;
  --accent-2: #7c6cff;
  --green: #3ecf8e;
  --radius: 14px;
}
/* theme sáng: mọi màu ghi đè qua biến, phần còn lại của file không đổi */
:root[data-theme="light"] {
  --bg: #f5f7fb;
  --bg-soft: #ffffff;
  --card: #ffffff;
  --card-2: #eef2f9;
  --line: #d8e0ec;
  --text: #182234;
  --muted: #5b6780;
  --accent: #2f6fd6;
  --accent-2: #6a55e8;
  --green: #159966;
}
* { box-sizing: border-box; }
[hidden] { display: none !important; } /* display:flex trong CSS sẽ đè attribute hidden nếu thiếu rule này */
html { scroll-behavior: smooth; }
body {
  margin: 0; background: var(--bg); color: var(--text);
  font: 16px/1.65 "Segoe UI", system-ui, -apple-system, Roboto, Arial, sans-serif;
}
a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }

/* nav */
.nav {
  position: sticky; top: 0; z-index: 50; display: flex; justify-content: space-between; align-items: center;
  padding: 14px 6vw; background: rgba(13, 18, 32, .85); backdrop-filter: blur(8px);
  border-bottom: 1px solid var(--line);
}
.nav-name { font-weight: 700; font-size: 18px; letter-spacing: .5px; }
.accent { color: var(--accent); }
.nav nav { display: flex; gap: 22px; }
.nav nav a { color: var(--muted); font-size: 14.5px; }
.nav nav a:hover { color: var(--text); text-decoration: none; }

main { max-width: 1080px; margin: 0 auto; padding: 0 6vw 60px; }
section { margin-top: 64px; }
h2 { font-size: 26px; margin: 0 0 18px; }
h2::after { content: ""; display: block; width: 46px; height: 3px; margin-top: 8px;
  background: linear-gradient(90deg, var(--accent), var(--accent-2)); border-radius: 2px; }

/* hero */
.hero { display: flex; gap: 32px; align-items: center; justify-content: space-between; flex-wrap: wrap;
  padding: 72px 0 8px; }
.hero h1 { font-size: 46px; margin: 0 0 6px; }
.hero-title { font-size: 21px; color: var(--accent); font-weight: 600; margin: 0 0 4px; }
.hero-loc { color: var(--muted); margin: 0 0 12px; }
.hero-links { display: flex; gap: 16px; flex-wrap: wrap; font-size: 14.5px; }
.hero-card { background: linear-gradient(145deg, var(--card), var(--card-2)); border: 1px solid var(--line);
  border-radius: var(--radius); padding: 22px 24px; max-width: 340px; }
.hero-card-title { font-weight: 700; margin: 0 0 6px; }
.hero-card-sub { color: var(--muted); font-size: 14px; margin: 0 0 14px; }
.btn { background: linear-gradient(90deg, var(--accent), var(--accent-2)); color: #fff; border: 0;
  padding: 10px 18px; border-radius: 10px; font-size: 15px; font-weight: 600; cursor: pointer; }
.btn:hover { filter: brightness(1.1); }

.about-text { color: var(--muted); max-width: 860px; font-size: 16.5px; }

/* skills */
.skills-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(300px, 1fr)); gap: 16px; }
.skill-cat { background: var(--card); border: 1px solid var(--line); border-radius: var(--radius); padding: 16px 18px; }
.skill-cat h3 { margin: 0 0 10px; font-size: 15.5px; color: var(--accent); }
.skill-cat .tags { display: flex; flex-wrap: wrap; gap: 7px; }
.tag { background: var(--bg-soft); border: 1px solid var(--line); color: var(--text);
  padding: 3px 10px; border-radius: 999px; font-size: 12.5px; }

/* timeline */
.timeline { border-left: 2px solid var(--line); margin-left: 8px; padding-left: 26px; }
.t-item { position: relative; margin-bottom: 30px; }
.t-item::before { content: ""; position: absolute; left: -33px; top: 7px; width: 12px; height: 12px;
  border-radius: 50%; background: var(--accent); box-shadow: 0 0 0 4px rgba(91, 157, 255, .18); }
.t-head { display: flex; justify-content: space-between; gap: 14px; flex-wrap: wrap; }
.t-role { font-weight: 700; font-size: 17px; }
.t-period { color: var(--muted); font-size: 13.5px; white-space: nowrap; }
.t-org { color: var(--accent); font-size: 14.5px; margin: 2px 0 4px; }
.t-stack { color: var(--muted); font-size: 13.5px; font-style: italic; margin: 0 0 8px; }
.t-item ul { margin: 0; padding-left: 18px; color: var(--muted); }
.t-item li { margin-bottom: 5px; }
.t-item li::marker { color: var(--accent); }

/* projects */
.projects-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(310px, 1fr)); gap: 16px; }
.proj { background: var(--card); border: 1px solid var(--line); border-radius: var(--radius);
  padding: 18px 20px; display: flex; flex-direction: column; gap: 10px; transition: transform .15s, border-color .15s; }
.proj:hover { transform: translateY(-3px); border-color: var(--accent); }
.proj h3 { margin: 0; font-size: 16.5px; }
.proj h3 a::after { content: " ↗"; font-size: 12px; color: var(--muted); }
.proj p { color: var(--muted); font-size: 14px; margin: 0; flex: 1; }
.proj .tags { display: flex; flex-wrap: wrap; gap: 6px; }

/* awards */
.awards { list-style: none; padding: 0; margin: 0; }
.awards li { background: var(--card); border: 1px solid var(--line); border-radius: var(--radius);
  padding: 14px 18px; margin-bottom: 10px; color: var(--muted); font-size: 14.5px; }
.awards li::before { content: "🏅 "; }

footer { border-top: 1px solid var(--line); color: var(--muted); text-align: center;
  padding: 26px 6vw 34px; font-size: 13.5px; }

/* chat */
.chat-fab { position: fixed; right: 22px; bottom: 22px; z-index: 100; width: 56px; height: 56px;
  border-radius: 50%; border: 0; font-size: 24px; cursor: pointer;
  background: linear-gradient(135deg, var(--accent), var(--accent-2)); color: #fff;
  box-shadow: 0 6px 20px rgba(91, 157, 255, .35); }
.chat-panel { position: fixed; right: 22px; bottom: 22px; z-index: 101; width: min(400px, calc(100vw - 32px));
  height: min(600px, calc(100vh - 44px)); display: flex; flex-direction: column;
  background: var(--bg-soft); border: 1px solid var(--line); border-radius: 16px; overflow: hidden;
  box-shadow: 0 12px 40px rgba(0, 0, 0, .5); }
.chat-head { display: flex; justify-content: space-between; align-items: center; padding: 12px 16px;
  background: linear-gradient(90deg, var(--card-2), var(--card)); border-bottom: 1px solid var(--line); }
.chat-head small { display: block; color: var(--muted); font-size: 12px; }
.chat-close { background: none; border: 0; color: var(--muted); font-size: 16px; cursor: pointer; }
.chat-msgs { flex: 1; overflow-y: auto; padding: 14px; display: flex; flex-direction: column; gap: 10px; }
.msg { max-width: 88%; padding: 9px 13px; border-radius: 12px; font-size: 14.5px; white-space: pre-wrap;
  overflow-wrap: anywhere; }
.msg.user { align-self: flex-end; background: linear-gradient(135deg, var(--accent), var(--accent-2)); color: #fff;
  border-bottom-right-radius: 4px; }
.msg.bot { align-self: flex-start; background: var(--card); border: 1px solid var(--line);
  border-bottom-left-radius: 4px; }
.msg.bot.error { border-color: #b00020; color: #ff9aa5; }
.chat-chips { display: flex; gap: 7px; flex-wrap: wrap; padding: 0 14px 10px; }
.chip { background: var(--card); border: 1px solid var(--line); color: var(--muted); border-radius: 999px;
  padding: 4px 11px; font-size: 12.5px; cursor: pointer; }
.chip:hover { color: var(--text); border-color: var(--accent); }
.chat-input { display: flex; gap: 8px; padding: 10px 12px; border-top: 1px solid var(--line); }
.chat-input input { flex: 1; background: var(--card); border: 1px solid var(--line); color: var(--text);
  border-radius: 10px; padding: 10px 12px; font-size: 14.5px; outline: none; }
.chat-input input:focus { border-color: var(--accent); }
.chat-input button { background: var(--accent); border: 0; color: #fff; border-radius: 10px; width: 42px;
  font-size: 16px; cursor: pointer; }

@media (max-width: 720px) {
  .hero h1 { font-size: 34px; }
  .hero { padding-top: 40px; }
  .nav nav { gap: 12px; font-size: 13px; }
  .book-grid { grid-template-columns: 1fr; }
}

/* ── theme toggle ─────────────────────────────────────────── */
.theme-toggle { background: var(--card); border: 1px solid var(--line); color: var(--text);
  border-radius: 10px; width: 34px; height: 34px; font-size: 16px; cursor: pointer; }
.nav-book { color: var(--green) !important; font-weight: 600; }

/* ── booking ──────────────────────────────────────────────── */
.book-note { color: var(--muted); max-width: 760px; }
.book-grid { display: grid; grid-template-columns: 340px 1fr; gap: 18px; align-items: start; }
.card { background: var(--card); border: 1px solid var(--line); border-radius: var(--radius); padding: 18px 20px; }
.cal-head { display: flex; justify-content: space-between; align-items: center; margin-bottom: 10px; }
.cal-head button { background: var(--bg-soft); border: 1px solid var(--line); color: var(--text);
  border-radius: 8px; width: 30px; height: 30px; font-size: 18px; cursor: pointer; }
.cal-dow, .cal-days { display: grid; grid-template-columns: repeat(7, 1fr); gap: 4px; text-align: center; }
.cal-dow span { color: var(--muted); font-size: 12px; padding: 2px 0; }
.cal-days button { position: relative; background: var(--bg-soft); border: 1px solid var(--line);
  color: var(--text); border-radius: 9px; padding: 9px 0; font-size: 14px; cursor: pointer; }
.cal-days button:disabled { opacity: .3; cursor: default; }
.cal-days button.sel { border-color: var(--accent); background: var(--accent); color: #fff; }
.cal-days button.avail::after { content: ""; position: absolute; bottom: 4px; left: 50%;
  transform: translateX(-50%); width: 5px; height: 5px; border-radius: 50%; background: var(--green); }
.cal-days .pad { border: 0; background: none; }
#slot-date, .book-form h3 { margin: 0 0 10px; font-size: 16px; }
.slots { display: flex; flex-wrap: wrap; gap: 8px; }
.slot { background: var(--bg-soft); border: 1px solid var(--line); color: var(--text); border-radius: 9px;
  padding: 7px 12px; font-size: 14px; cursor: pointer; }
.slot:hover { border-color: var(--accent); }
.slot small { display: block; color: var(--muted); font-size: 10.5px; }
.book-form { display: flex; flex-direction: column; gap: 10px; margin-top: 14px; }
.book-form label { font-size: 13.5px; color: var(--muted); display: flex; flex-direction: column; gap: 4px; }
.book-form input, .book-form textarea { background: var(--bg-soft); border: 1px solid var(--line);
  color: var(--text); border-radius: 9px; padding: 9px 11px; font: inherit; font-size: 14px; outline: none; }
.book-form input:focus, .book-form textarea:focus { border-color: var(--accent); }
.book-form .hp { position: absolute; left: -9999px; }
.book-done p { color: var(--muted); font-size: 14.5px; }
.book-done a.btn, .book-done a.slot { display: inline-block; }
.book-done .row { display: flex; gap: 10px; flex-wrap: wrap; margin-top: 12px; }
.btn.ghost { background: var(--bg-soft); border: 1px solid var(--line); color: var(--text); }
.book-empty { color: var(--muted); font-size: 14.5px; }
.badge { display: inline-block; background: rgba(62, 207, 142, .15); color: var(--green);
  border: 1px solid var(--green); border-radius: 999px; font-size: 12px; padding: 2px 10px; }