/* =========================================================
   TOKENS
   ========================================================= */
:root {
  --bg: #0B1120;
  --surface: #121A2C;
  --surface-2: #17213A;
  --border: rgba(148, 163, 184, 0.16);
  --border-strong: rgba(148, 163, 184, 0.30);
  --ink: #E9ECF4;
  --muted: #8B93A8;
  --signal: #3D8FE8;      /* blue — "flagged / watch this" accent */
  --signal-ink: #0B1120;
  --signal-glow: rgba(61, 143, 232, 0.22);
  --stable: #4FB8A6;      /* teal — secondary / "stable" accent */
  --grid-line: rgba(148, 163, 184, 0.07);
  --shadow: 0 20px 44px rgba(0,0,0,0.34);

  --font-display: "Space Grotesk", "Segoe UI", sans-serif;
  --font-body: "IBM Plex Sans", "Segoe UI", sans-serif;
  --font-mono: "IBM Plex Mono", "Courier New", monospace;

  --node-gutter: 2.5rem;
  --max-width: 1120px;
  --radius: 12px;
  --radius-sm: 8px;
}

html[data-theme="light"] {
  --bg: #F1F3F8;
  --surface: #FFFFFF;
  --surface-2: #E8EBF3;
  --border: rgba(15, 23, 42, 0.10);
  --border-strong: rgba(15, 23, 42, 0.20);
  --ink: #10131C;
  --muted: #5B6478;
  --signal: #0A5FB5;
  --signal-ink: #FFFFFF;
  --signal-glow: rgba(10, 95, 181, 0.16);
  --stable: #2E8F81;
  --grid-line: rgba(15, 23, 42, 0.05);
  --shadow: 0 20px 44px rgba(15, 23, 42, 0.10);
}

/* =========================================================
   RESET & BASE
   ========================================================= */
* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font-family: var(--font-body);
  font-size: 16px;
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
  transition: background-color .35s ease, color .35s ease;
}
h1, h2, h3 { font-family: var(--font-display); margin: 0 0 1rem; color: var(--ink); }
p { margin: 0 0 1rem; color: var(--ink); }
a { color: inherit; text-decoration: none; }
ul { list-style: none; margin: 0; padding: 0; }
svg.icon { width: 18px; height: 18px; flex-shrink: 0; }
button { font-family: inherit; cursor: pointer; background: none; border: none; color: inherit; }

:focus-visible {
  outline: 2px solid var(--signal);
  outline-offset: 3px;
  border-radius: 4px;
}

/* language switching: each bilingual node has <span lang="vi"> + <span lang="en"> siblings */
html[data-lang="vi"] [lang="en"] { display: none; }
html[data-lang="en"] [lang="vi"] { display: none; }

/* background grid */
.bg-grid {
  position: fixed;
  inset: 0;
  z-index: -1;
  pointer-events: none;
  background-image:
    linear-gradient(to right, var(--grid-line) 1px, transparent 1px),
    linear-gradient(to bottom, var(--grid-line) 1px, transparent 1px);
  background-size: 48px 48px;
  -webkit-mask-image: radial-gradient(ellipse 75% 55% at 50% 0%, black 35%, transparent 85%);
          mask-image: radial-gradient(ellipse 75% 55% at 50% 0%, black 35%, transparent 85%);
}

/* =========================================================
   NAV
   ========================================================= */
.nav {
  position: sticky;
  top: 0;
  z-index: 40;
  background: color-mix(in srgb, var(--bg) 78%, transparent);
  -webkit-backdrop-filter: blur(10px);
  backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--border);
}
.nav-inner {
  max-width: var(--max-width);
  margin-inline: auto;
  padding: 0.9rem clamp(1.25rem, 4vw, 2.5rem);
  display: flex;
  align-items: center;
  gap: 2rem;
}
.logo {
  font-family: var(--font-display);
  font-weight: 700;
  font-size: 1.05rem;
  letter-spacing: 0.02em;
  display: inline-flex;
  align-items: center;
  white-space: nowrap;
}
.logo-short { display: none; }
.logo-dot {
  width: 6px; height: 6px; border-radius: 50%;
  background: var(--signal);
  margin-left: 5px;
}
.nav-links {
  display: flex;
  gap: 1.75rem;
  margin-right: auto;
  font-family: var(--font-mono);
  font-size: 0.82rem;
  text-transform: lowercase;
  letter-spacing: 0.02em;
}
.nav-links a {
  color: var(--muted);
  position: relative;
  padding: 0.3rem 0;
  transition: color .2s ease;
}
.nav-links a:hover { color: var(--ink); }
.nav-links a.is-active { color: var(--signal); }
.nav-links a.is-active::before {
  content: "";
  position: absolute;
  left: -0.85rem;
  top: 50%;
  transform: translateY(-50%);
  width: 5px; height: 5px;
  border-radius: 50%;
  background: var(--signal);
}

.nav-actions { display: flex; align-items: center; gap: 0.6rem; }

.btn-cv {
  font-family: var(--font-mono);
  font-size: 0.78rem;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  background: var(--signal);
  color: var(--signal-ink);
  padding: 0.5rem 0.95rem;
  border-radius: 999px;
  font-weight: 500;
  transition: transform .2s ease, box-shadow .2s ease;
  white-space: nowrap;
}
.btn-cv:hover { transform: translateY(-1px); box-shadow: 0 8px 20px var(--signal-glow); }

.btn-cert {
  font-family: var(--font-mono);
  font-size: 0.78rem;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  background: transparent;
  color: var(--ink);
  border: 1px solid var(--border-strong);
  padding: 0.5rem 0.95rem;
  border-radius: 999px;
  font-weight: 500;
  transition: border-color .2s ease, color .2s ease, transform .2s ease;
  white-space: nowrap;
}
.btn-cert:hover {
  border-color: var(--signal);
  color: var(--signal);
  transform: translateY(-1px);
}

.lang-toggle {
  display: flex;
  border: 1px solid var(--border-strong);
  border-radius: 999px;
  overflow: hidden;
  font-family: var(--font-mono);
  font-size: 0.72rem;
  letter-spacing: 0.04em;
}
.lang-pill {
  padding: 0.42rem 0.65rem;
  color: var(--muted);
  transition: background .2s ease, color .2s ease;
}
html[data-lang="vi"] .lang-pill[data-lang-target="vi"],
html[data-lang="en"] .lang-pill[data-lang-target="en"] {
  background: var(--surface-2);
  color: var(--ink);
}

.theme-toggle, .menu-toggle {
  width: 34px; height: 34px;
  display: inline-flex; align-items: center; justify-content: center;
  border: 1px solid var(--border-strong);
  border-radius: 999px;
  color: var(--ink);
}
html[data-theme="dark"] .icon-sun { display: none; }
html[data-theme="light"] .icon-moon { display: none; }

.menu-toggle { display: none; }
.icon-close { display: none; }
.menu-toggle[aria-expanded="true"] .icon-burger { display: none; }
.menu-toggle[aria-expanded="true"] .icon-close { display: inline-block; }

.nav-mobile {
  display: none;
  flex-direction: column;
  padding: 0.5rem clamp(1.25rem, 4vw, 2.5rem) 1.25rem;
  font-family: var(--font-mono);
  font-size: 0.95rem;
  border-top: 1px solid var(--border);
}
.nav-mobile a { padding: 0.7rem 0; color: var(--muted); border-bottom: 1px solid var(--border); }
.nav-mobile a.is-active { color: var(--signal); }

/* =========================================================
   PIPELINE / RAIL
   ========================================================= */
.pipeline {
  max-width: var(--max-width);
  margin-inline: auto;
  padding-inline: clamp(1.25rem, 4vw, 2.5rem);
  position: relative;
}
.rail { position: absolute; inset: 0; pointer-events: none; }
.rail-line {
  position: absolute;
  top: 0; bottom: 0;
  left: calc(var(--node-gutter) / 2 - 1px);
  width: 2px;
  background: var(--border);
}

.section {
  position: relative;
  padding-block: clamp(3.5rem, 8vw, 6.5rem);
  border-top: 1px solid transparent;
}

.eyebrow {
  display: grid;
  grid-template-columns: var(--node-gutter) auto;
  align-items: center;
  column-gap: 0.75rem;
  margin-bottom: 1.25rem;
}
.node {
  justify-self: center;
  width: 11px; height: 11px;
  border-radius: 50%;
  background: var(--bg);
  border: 2px solid var(--muted);
  transition: background .3s ease, border-color .3s ease, box-shadow .3s ease;
}
.section.is-active .node {
  border-color: var(--signal);
  background: var(--signal);
  box-shadow: 0 0 0 5px var(--signal-glow);
}
.eyebrow .tag {
  font-family: var(--font-mono);
  font-size: 0.75rem;
  text-transform: uppercase;
  letter-spacing: 0.16em;
  color: var(--muted);
  transition: color .3s ease;
}
.section.is-active .eyebrow .tag { color: var(--signal); }

.section > h1, .section > h2, .section > .about-grid,
.section > .skills-grid, .section > .projects-grid,
.section > .contact-lede, .section > .contact-grid {
  margin-left: var(--node-gutter);
}

/* =========================================================
   ABOUT
   ========================================================= */
.hero-heading {
  font-size: clamp(2.1rem, 4.4vw, 3.4rem);
  font-weight: 600;
  line-height: 1.12;
  letter-spacing: -0.01em;
  max-width: 22ch;
  margin-bottom: 2.75rem;
}

.about-grid {
  display: grid;
  grid-template-columns: 220px 1fr;
  gap: clamp(1.75rem, 4vw, 3rem);
  align-items: start;
}
.photo-frame {
  aspect-ratio: 4 / 5;
  border: 1.5px dashed var(--border-strong);
  border-radius: var(--radius);
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 0.6rem;
  color: var(--muted);
  background: var(--surface);
  overflow: hidden;
}
.photo-frame img { width: 100%; height: 100%; object-fit: cover; }
.photo-icon { width: 34px; height: 34px; opacity: 0.7; }
.photo-hint { font-family: var(--font-mono); font-size: 0.75rem; }

.about-copy p { color: var(--muted); font-size: 1.02rem; }
.about-copy strong { color: var(--ink); font-weight: 600; }

/* =========================================================
   SKILLS
   ========================================================= */
.skills-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 1.1rem;
}
.skill-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.35rem 1.25rem;
  transition: border-color .2s ease, transform .2s ease;
}
.skill-card:hover { border-color: var(--border-strong); transform: translateY(-2px); }
.skill-card h3 {
  font-family: var(--font-mono);
  font-size: 0.78rem;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--muted);
  font-weight: 500;
  margin-bottom: 0.9rem;
}
.tag-list { display: flex; flex-direction: column; gap: 0.55rem; }
.tag-list li {
  font-size: 0.92rem;
  color: var(--ink);
  padding-left: 0.9rem;
  position: relative;
}
.tag-list li::before {
  content: "";
  position: absolute; left: 0; top: 0.55em;
  width: 4px; height: 4px; border-radius: 50%;
  background: var(--stable);
}
.tag-list--inline { flex-direction: row; flex-wrap: wrap; gap: 0.5rem; }
.tag-list--inline li {
  padding: 0.28rem 0.7rem;
  border: 1px solid var(--border-strong);
  border-radius: 999px;
  font-family: var(--font-mono);
  font-size: 0.75rem;
  color: var(--muted);
}
.tag-list--inline li::before { display: none; }

/* =========================================================
   PROJECTS
   ========================================================= */
.projects-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 1.5rem;
}
.project-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  overflow: hidden;
  transition: border-color .2s ease, transform .2s ease, box-shadow .2s ease;
}
.project-card:hover { border-color: var(--border-strong); transform: translateY(-3px); box-shadow: var(--shadow); }
.project-thumb {
  aspect-ratio: 16 / 9;
  border-bottom: 1px dashed var(--border-strong);
  display: flex; align-items: center; justify-content: center;
  color: var(--muted);
  font-family: var(--font-mono);
  font-size: 0.8rem;
  background: var(--surface-2);
}
.project-thumb img { width: 100%; height: 100%; object-fit: cover; }
.project-body { padding: 1.35rem 1.4rem 1.5rem; }
.project-body h3 { font-size: 1.1rem; margin-bottom: 0.55rem; }
.project-body p { color: var(--muted); font-size: 0.94rem; margin-bottom: 1rem; }
.project-links { margin-top: 1.1rem; }
.project-links a {
  display: inline-flex; align-items: center; gap: 0.4rem;
  font-family: var(--font-mono);
  font-size: 0.8rem;
  color: var(--ink);
  border-bottom: 1px solid var(--border-strong);
  padding-bottom: 2px;
  transition: color .2s ease, border-color .2s ease;
}
.project-links a:hover { color: var(--signal); border-color: var(--signal); }

/* =========================================================
   CONTACT
   ========================================================= */
.contact-lede { color: var(--muted); max-width: 46ch; margin-bottom: 2rem; font-size: 1.02rem; }
.contact-grid { display: flex; flex-direction: column; gap: 0.75rem; max-width: 480px; }
.contact-row {
  display: flex; align-items: center; gap: 0.9rem;
  padding: 0.95rem 1.1rem;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  background: var(--surface);
  transition: border-color .2s ease, transform .2s ease;
}
.contact-row:hover { border-color: var(--signal); transform: translateX(3px); }
.contact-row .icon { color: var(--stable); }
.contact-label {
  font-family: var(--font-mono);
  font-size: 0.72rem;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--muted);
  width: 70px;
  flex-shrink: 0;
}
.contact-value { font-size: 0.94rem; color: var(--ink); }

/* =========================================================
   FOOTER
   ========================================================= */
.site-footer {
  max-width: var(--max-width);
  margin-inline: auto;
  padding: 2rem clamp(1.25rem, 4vw, 2.5rem) 3rem;
  display: flex; flex-wrap: wrap; gap: 0.5rem;
  font-family: var(--font-mono);
  font-size: 0.78rem;
  color: var(--muted);
  border-top: 1px solid var(--border);
}
.footer-sep { opacity: 0.5; }

/* =========================================================
   SCROLL REVEAL + MOTION (respects prefers-reduced-motion)
   ========================================================= */
@media (prefers-reduced-motion: no-preference) {
  .section { opacity: 0; transform: translateY(18px); transition: opacity .6s ease, transform .6s ease; }
  .section.is-revealed { opacity: 1; transform: none; }

  .hero-heading, .about-grid { opacity: 0; transform: translateY(14px); }
  body.is-ready .hero-heading { opacity: 1; transform: none; transition: opacity .7s ease .1s, transform .7s ease .1s; }
  body.is-ready .about-grid { opacity: 1; transform: none; transition: opacity .7s ease .25s, transform .7s ease .25s; }
}

/* =========================================================
   RESPONSIVE
   ========================================================= */
@media (max-width: 900px) {
  .skills-grid { grid-template-columns: repeat(2, 1fr); }
  .projects-grid { grid-template-columns: 1fr; }
}

@media (max-width: 760px) {
  .nav-links { display: none; }
  .menu-toggle { display: inline-flex; }
  .nav-mobile.is-open { display: flex; }
  .btn-cv span { display: inline; }

  .logo-full { display: none; }
  .logo-short { display: inline; }

  :root { --node-gutter: 0px; }
  .rail, .node { display: none; }
  .eyebrow { grid-template-columns: 1fr; }
  .section > h1, .section > h2, .section > .about-grid,
  .section > .skills-grid, .section > .projects-grid,
  .section > .contact-lede, .section > .contact-grid {
    margin-left: 0;
  }

  .about-grid { grid-template-columns: 1fr; }
  .photo-frame { max-width: 200px; }
  .skills-grid { grid-template-columns: 1fr 1fr; }
}

@media (max-width: 480px) {
  .skills-grid { grid-template-columns: 1fr; }
  .btn-cv { padding: 0.5rem 0.75rem; }
  .nav-inner { gap: 1rem; }
}