/* =========================================================
   Viet-Hoang Dong — personal site
   Warm scholar palette (cream / navy), serif academic.
   ========================================================= */

:root {
  /* Warm latte / slow-afternoon palette */
  --bg:            #F7EDD7;
  --bg-elev:       #FDF6E2;
  --ink:           #2B2520;
  --ink-muted:     #7A6A5A;
  --rule:          #E4D4B2;
  --navy:          #3C5A75;
  --navy-soft:     #567890;
  --accent:        #B87333;
  --accent-soft:   #D29559;
  --code-bg:       #F0E4C6;
  --shadow:        0 1px 0 rgba(60,90,117,.05), 0 12px 36px rgba(120,90,50,.10);

  --f-serif: "Source Serif 4","Source Serif Pro","EB Garamond",Georgia,"Times New Roman",serif;
  --f-sans:  "Inter",-apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,sans-serif;
  --f-mono:  "JetBrains Mono",ui-monospace,SFMono-Regular,Menlo,Consolas,monospace;

  --maxw: 980px;
  --gutter: clamp(1.25rem, 3vw, 2rem);
}

[data-theme="dark"] {
  /* Warm cocoa-navy night with amber warmth */
  --bg:            #1C1A1E;
  --bg-elev:       #252327;
  --ink:           #EFE1C6;
  --ink-muted:     #A89A85;
  --rule:          #3A3531;
  --navy:          #E7CFA0;
  --navy-soft:     #C9B485;
  --accent:        #E6A55C;
  --accent-soft:   #F0BE84;
  --code-bg:       #2E2A26;
  --shadow:        0 1px 0 rgba(0,0,0,.3), 0 14px 40px rgba(0,0,0,.45);
}

/* -------- Reset-ish -------- */
*,*::before,*::after{box-sizing:border-box}
html{scroll-behavior:smooth}
body{
  margin:0;
  background:
    radial-gradient(ellipse at 15% -10%, color-mix(in oklab,var(--accent-soft) 18%,transparent), transparent 55%),
    radial-gradient(ellipse at 90% 110%, color-mix(in oklab,var(--navy-soft) 14%,transparent), transparent 55%),
    var(--bg);
  background-attachment: fixed;
  color:var(--ink);
  font-family:var(--f-serif);
  font-size:18px;
  line-height:1.7;
  -webkit-font-smoothing:antialiased;
  text-rendering:optimizeLegibility;
  transition:background .4s ease, color .4s ease;
}
img{max-width:100%;display:block}
/* Animated underline wipe — left-to-right on hover. */
a{
  color:var(--navy);
  text-decoration:none;
  background-image:linear-gradient(to right,var(--accent),var(--accent));
  background-size:0% 1.5px;
  background-repeat:no-repeat;
  background-position:0 100%;
  padding-bottom:1px;
  transition:background-size .4s cubic-bezier(.2,.7,.2,1), color .2s ease;
}
a:hover{color:var(--accent);background-size:100% 1.5px}
hr{border:0;border-top:1px solid var(--rule);margin:2.5rem 0}

h1,h2,h3,h4{
  font-family:var(--f-serif);
  color:var(--ink);
  letter-spacing:-0.01em;
  line-height:1.2;
  margin:0 0 .6em;
  font-weight:600;
}
h1{font-size:clamp(2rem,4vw,2.9rem);font-weight:700}
h2{font-size:clamp(1.5rem,2.6vw,1.9rem);margin-top:2.6rem}
h3{font-size:1.22rem;margin-top:1.8rem}
p{margin:0 0 1em}

.small{font-size:.9rem;color:var(--ink-muted)}
.muted{color:var(--ink-muted)}
.eyebrow{
  font-family:var(--f-sans);
  font-size:.72rem;
  letter-spacing:.22em;
  text-transform:uppercase;
  color:var(--accent);
  font-weight:600;
}

/* -------- Layout -------- */
.container{max-width:var(--maxw);margin:0 auto;padding:0 var(--gutter)}
main{padding:3rem 0 5rem}
section{margin-bottom:3.2rem}

/* -------- Nav -------- */
.nav{
  position:sticky;top:0;z-index:30;
  backdrop-filter:saturate(140%) blur(10px);
  background:color-mix(in oklab,var(--bg) 82%,transparent);
  border-bottom:1px solid var(--rule);
}
.nav-inner{
  display:flex;align-items:center;justify-content:space-between;
  max-width:var(--maxw);margin:0 auto;padding:.9rem var(--gutter);
}
.brand{
  font-weight:700;letter-spacing:.01em;color:var(--ink);
  border:0;font-size:1.05rem;background-image:none;padding:0;
  display:inline-flex;align-items:center;gap:.6rem;
}
.brand:hover{color:var(--accent)}
.brand-mark{
  width:30px;height:30px;flex-shrink:0;display:inline-flex;
  align-items:center;justify-content:center;
}
.brand-mark svg{max-width:100%;height:auto}

/* Hero 3D mark — replaces .portrait on the home page */
.hero-mark{
  justify-self:end;
  width:280px;height:280px;
  display:flex;align-items:center;justify-content:center;
  position:relative;
}
.hero-mark svg{max-width:100%;height:auto}
@media (max-width:720px){
  .hero-mark{justify-self:start;width:200px;height:200px}
}
.brand .dot{color:var(--accent)}
.nav-links{display:flex;gap:1.4rem;align-items:center;font-family:var(--f-sans);font-size:.93rem}
.nav-links a{color:var(--ink-muted);border:0;position:relative;padding:.3rem 0;background-image:none}
.nav-links a.active,.nav-links a:hover{color:var(--ink)}
.nav-links a.active::after{
  content:"";position:absolute;left:0;right:0;bottom:-2px;height:2px;
  background:var(--accent);border-radius:2px;
}

.theme-toggle{
  background:transparent;border:1px solid var(--rule);color:var(--ink);
  width:38px;height:38px;border-radius:50%;cursor:pointer;
  display:inline-flex;align-items:center;justify-content:center;
  transition:background .2s, transform .15s;
}
.theme-toggle:hover{background:var(--bg-elev);transform:rotate(18deg)}
.theme-toggle svg{width:18px;height:18px}
.theme-toggle .sun{display:none}
[data-theme="dark"] .theme-toggle .moon{display:none}
[data-theme="dark"] .theme-toggle .sun{display:inline}

.mobile-toggle{display:none;background:none;border:0;color:var(--ink);font-size:1.5rem;cursor:pointer}

@media (max-width:720px){
  .mobile-toggle{display:inline-block}
  .nav-links{
    position:absolute;top:100%;left:0;right:0;
    flex-direction:column;gap:0;align-items:stretch;
    background:var(--bg-elev);border-bottom:1px solid var(--rule);
    max-height:0;overflow:hidden;transition:max-height .25s ease;
  }
  .nav-links.open{max-height:400px}
  .nav-links a{padding:1rem var(--gutter);border-bottom:1px solid var(--rule)}
  .nav-links a.active::after{display:none}
}

/* -------- Hero -------- */
.hero{
  display:grid;
  grid-template-columns:1.4fr 1fr;
  gap:3rem;
  align-items:center;
  padding:3rem 0 1.5rem;
}
.hero h1{margin-bottom:.5rem}
.hero .tagline{
  font-style:italic;color:var(--ink-muted);font-size:1.15rem;margin-bottom:1.2rem;
}
.hero .bio{font-size:1.02rem;color:var(--ink)}
.hero .portrait{
  width:240px;height:240px;justify-self:end;
  border-radius:50%;
  background:linear-gradient(145deg,var(--navy),var(--accent));
  display:flex;align-items:center;justify-content:center;
  color:var(--bg);font-family:var(--f-serif);font-size:5rem;font-weight:700;
  box-shadow:var(--shadow);
  border:4px solid var(--bg-elev);
  overflow:hidden;
}
.hero .portrait img{width:100%;height:100%;object-fit:cover}

@media (max-width:720px){
  .hero{grid-template-columns:1fr;gap:1.5rem;padding-top:1.5rem}
  .hero .portrait{justify-self:start;width:170px;height:170px;font-size:3.5rem}
}

/* -------- Socials -------- */
.socials{display:flex;gap:1rem;flex-wrap:wrap;margin-top:1.2rem;font-family:var(--f-sans);font-size:.9rem}
.socials a{
  display:inline-flex;align-items:center;gap:.4rem;
  padding:.45rem .85rem;border-radius:999px;
  border:1px solid var(--rule);color:var(--ink);
  background-image:none;
  transition:background .2s, border-color .2s, color .2s, transform .2s;
}
.socials a:hover{background:var(--bg-elev);border-color:var(--accent);color:var(--accent);transform:translateY(-1px)}
.socials svg{width:15px;height:15px}

/* -------- Tag chips -------- */
.chips{display:flex;flex-wrap:wrap;gap:.45rem;margin-top:.6rem;font-family:var(--f-sans)}
.chip{
  font-size:.78rem;letter-spacing:.02em;
  padding:.28rem .7rem;border-radius:999px;
  background:var(--code-bg);color:var(--navy);
  border:1px solid var(--rule);
}

/* -------- Cards / grid -------- */
.grid{display:grid;gap:1.2rem}
.grid.cols-2{grid-template-columns:repeat(2,minmax(0,1fr))}
.grid.cols-3{grid-template-columns:repeat(3,minmax(0,1fr))}
@media (max-width:720px){.grid.cols-2,.grid.cols-3{grid-template-columns:1fr}}

.card{
  background:var(--bg-elev);
  border:1px solid var(--rule);
  border-radius:14px;
  padding:1.4rem 1.5rem;
  transition:transform .2s ease, box-shadow .2s ease, border-color .2s;
}
.card:hover{transform:translateY(-2px);box-shadow:var(--shadow);border-color:var(--accent-soft)}
.card h3{margin-top:0}
.card .meta{font-family:var(--f-sans);font-size:.82rem;color:var(--ink-muted);margin-bottom:.4rem}

/* -------- Publications -------- */
.pub-list{list-style:none;padding:0;margin:0}
.pub-list li{
  padding:1.25rem 0;
  border-bottom:1px dashed var(--rule);
}
.pub-list li:last-child{border-bottom:0}
.pub-venue{
  display:inline-block;font-family:var(--f-sans);font-size:.75rem;
  letter-spacing:.08em;text-transform:uppercase;color:var(--accent);
  margin-bottom:.3rem;font-weight:600;
}
.pub-title{font-weight:600;font-size:1.08rem;margin:.15rem 0}
.pub-authors{color:var(--ink-muted);font-size:.95rem;font-style:italic}
.pub-authors .me{color:var(--ink);font-style:normal;font-weight:600;border-bottom:2px solid var(--accent-soft)}
.pub-links{margin-top:.5rem;font-family:var(--f-sans);font-size:.82rem;display:flex;gap:.8rem;flex-wrap:wrap}
.pub-links a{
  color:var(--navy);
  background-image:linear-gradient(to right,var(--rule),var(--rule));
  background-size:100% 1px;background-position:0 100%;background-repeat:no-repeat;
}
.pub-links a:hover{
  background-image:linear-gradient(to right,var(--accent),var(--accent));
  background-size:100% 1.5px;color:var(--accent);
}

/* -------- Timeline (CV) -------- */
.timeline{position:relative;padding-left:1.4rem;border-left:2px solid var(--rule)}
.tl-item{position:relative;padding:0 0 1.8rem;margin-left:.4rem}
.tl-item::before{
  content:"";position:absolute;left:-2rem;top:.55rem;
  width:11px;height:11px;border-radius:50%;
  background:var(--accent);border:2px solid var(--bg);
}
.tl-date{font-family:var(--f-sans);font-size:.82rem;color:var(--ink-muted);letter-spacing:.04em}
.tl-title{font-weight:600;font-size:1.05rem;margin:.15rem 0}
.tl-org{color:var(--navy);font-style:italic}
.tl-body{margin-top:.5rem;color:var(--ink-muted);font-size:.97rem}
.tl-body ul{margin:.4rem 0 0;padding-left:1.1rem}
.tl-body li{margin-bottom:.25rem}

/* -------- Ventures -------- */
.venture{
  display:grid;grid-template-columns:auto 1fr;gap:1rem 1.3rem;
  padding:1.4rem;border:1px solid var(--rule);border-radius:14px;background:var(--bg-elev);
}
.venture + .venture{margin-top:1rem}
.venture .logo{
  width:64px;height:64px;border-radius:14px;
  display:flex;align-items:center;justify-content:center;
  background:var(--bg);
  color:var(--navy);font-weight:700;font-size:1.4rem;
  font-family:var(--f-sans);
  border:1px solid var(--rule);
  overflow:hidden;
  box-shadow:0 1px 0 rgba(0,0,0,.03);
}
.venture .logo img{
  width:100%;height:100%;object-fit:contain;padding:6px;
  display:block;
}
.venture h3{margin:0 0 .2rem}
.venture .role{font-family:var(--f-sans);font-size:.78rem;letter-spacing:.08em;
  text-transform:uppercase;color:var(--accent);font-weight:600}

/* -------- News -------- */
.news{list-style:none;padding:0;margin:0;border-top:1px solid var(--rule)}
.news li{display:grid;grid-template-columns:110px 1fr;gap:1rem;padding:.9rem 0;border-bottom:1px solid var(--rule);font-size:.98rem}
.news .date{font-family:var(--f-sans);font-size:.82rem;color:var(--accent);font-weight:600;letter-spacing:.05em}
@media (max-width:520px){.news li{grid-template-columns:1fr;gap:.1rem}}

/* -------- Footer -------- */
footer{
  border-top:1px solid var(--rule);
  padding:2rem 0 3rem;color:var(--ink-muted);
  font-family:var(--f-sans);font-size:.86rem;
}
footer .container{display:flex;justify-content:space-between;flex-wrap:wrap;gap:1rem}

/* -------- Utility -------- */
.btn{
  display:inline-block;padding:.6rem 1.1rem;border-radius:999px;
  font-family:var(--f-sans);font-size:.88rem;font-weight:500;
  background:var(--navy);color:var(--bg);border:1px solid var(--navy);
  background-image:none;
}
.btn:hover{background:var(--accent);border-color:var(--accent);color:var(--bg)}
.btn.ghost{background:transparent;color:var(--ink);border-color:var(--rule)}
.btn.ghost:hover{border-color:var(--accent);color:var(--accent);background:transparent}

/* ===== Animations ===== */

/* #2 — Hero word-by-word reveal */
.reveal-word{
  display:inline-block;
  opacity:0;
  transform:translateY(10px);
  transition:opacity .55s cubic-bezier(.2,.7,.2,1),
             transform .55s cubic-bezier(.2,.7,.2,1);
  will-change:opacity,transform;
}
.reveal-word.in{opacity:1;transform:translateY(0)}

/* #3 — Scroll-triggered section reveal */
.reveal{
  opacity:0;
  transform:translateY(22px);
  transition:opacity .8s cubic-bezier(.2,.7,.2,1),
             transform .8s cubic-bezier(.2,.7,.2,1);
  will-change:opacity,transform;
}
.reveal.in-view{opacity:1;transform:translateY(0)}

/* #6 — Graph-paper research hero */
.research-hero{
  position:relative;
  padding:3.25rem 2rem 3rem;
  border-radius:18px;
  margin-bottom:2rem;
  isolation:isolate;
  overflow:hidden;
  background:color-mix(in oklab,var(--bg-elev) 80%,transparent);
  border:1px solid var(--rule);
}
.research-hero::before{
  content:"";
  position:absolute;inset:-20%;z-index:-1;
  background-image:
    linear-gradient(to right, color-mix(in oklab,var(--navy) 18%,transparent) 1px, transparent 1px),
    linear-gradient(to bottom,color-mix(in oklab,var(--navy) 18%,transparent) 1px, transparent 1px);
  background-size:34px 34px;
  opacity:.35;
  animation:grid-drift 42s linear infinite;
}
.research-hero::after{
  content:"";
  position:absolute;inset:0;z-index:-1;
  background:radial-gradient(ellipse at 30% 0%,
              color-mix(in oklab,var(--bg-elev) 95%,transparent) 10%,
              transparent 70%);
}
@keyframes grid-drift{
  from{transform:translate(0,0)}
  to  {transform:translate(34px,34px)}
}

/* Respect reduced-motion users */
@media (prefers-reduced-motion: reduce){
  .reveal-word,.reveal{opacity:1!important;transform:none!important;transition:none!important}
  .research-hero::before{animation:none}
  html{scroll-behavior:auto}
  .badge-new::after, .pub-venue.hot::before { animation:none !important }
  .triad .edge.live { animation:none !important }
}

/* ===== #4 — Theme crossfade via View Transitions API ===== */
::view-transition-old(root),
::view-transition-new(root){
  animation:none; mix-blend-mode:normal;
}
::view-transition-new(root){
  animation:vt-reveal .55s cubic-bezier(.2,.7,.2,1) forwards;
}
::view-transition-old(root){
  animation:vt-hold .55s linear forwards;
  z-index:1;
}
::view-transition-new(root){ z-index:2 }
@keyframes vt-reveal{
  from{clip-path:circle(0 at var(--vt-x,50%) var(--vt-y,50%));}
  to  {clip-path:circle(var(--vt-r,100vmax) at var(--vt-x,50%) var(--vt-y,50%));}
}
@keyframes vt-hold{ from{opacity:1} to{opacity:1} }

/* ===== #5 — Pulse badge on hot publication ===== */
.badge-new{
  display:inline-block;
  position:relative;
  margin-left:.5rem;
  padding:.12rem .55rem;
  font-family:var(--f-sans);
  font-size:.66rem;letter-spacing:.16em;font-weight:700;
  color:var(--bg);
  background:var(--accent);
  border-radius:999px;
  vertical-align:1px;
}
.badge-new::after{
  content:"";
  position:absolute;inset:0;border-radius:999px;
  box-shadow:0 0 0 0 color-mix(in oklab, var(--accent) 60%, transparent);
  animation:pulse-ring 2.2s cubic-bezier(.2,.7,.2,1) infinite;
}
@keyframes pulse-ring{
  0%  {box-shadow:0 0 0 0 color-mix(in oklab, var(--accent) 55%, transparent);}
  70% {box-shadow:0 0 0 14px transparent;}
  100%{box-shadow:0 0 0 0 transparent;}
}
.pub-venue.hot{position:relative;z-index:0}
.pub-venue.hot::before{
  content:"";position:absolute;inset:-3px -7px;border-radius:5px;
  background:color-mix(in oklab, var(--accent-soft) 35%, transparent);
  z-index:-1;
  animation:pulse-glow 2.4s ease-in-out infinite;
}
@keyframes pulse-glow{
  0%,100%{opacity:.35}
  50%    {opacity:.85}
}

/* ===== #7 — Mini recommender graph (triad) ===== */
.triad-wrap{
  display:grid;
  grid-template-columns:1.1fr 1fr;
  gap:2rem;align-items:center;
  padding:1.6rem;
  background:var(--bg-elev);
  border:1px solid var(--rule);
  border-radius:16px;
}
.triad-wrap p{margin:0 0 .5em;color:var(--ink-muted);font-size:.98rem}
.triad-wrap h3{margin-top:0}
@media (max-width:720px){.triad-wrap{grid-template-columns:1fr}}

.triad{width:100%;height:auto;max-height:340px}
.triad .edge{
  stroke:var(--rule);stroke-width:2;
  stroke-dasharray:5 5;opacity:.7;
  transition:stroke .3s, stroke-width .3s, opacity .3s;
}
.triad .node circle{
  fill:var(--bg);stroke:var(--navy);stroke-width:2;
  transition:fill .25s, stroke .25s, r .25s, transform .25s;
  transform-box:fill-box;transform-origin:center;
}
.triad .node text{
  font-family:var(--f-serif);font-size:15px;font-weight:600;
  text-anchor:middle;dominant-baseline:central;
  fill:var(--ink);pointer-events:none;
  transition:fill .25s;
}
.triad .node{cursor:pointer}
.triad .node:hover circle{
  fill:var(--accent);stroke:var(--accent);
  transform:scale(1.08);
}
.triad .node:hover text{fill:var(--bg)}

.triad[data-active="user"]    .edge[data-pair~="user"],
.triad[data-active="item"]    .edge[data-pair~="item"],
.triad[data-active="review"]  .edge[data-pair~="review"]{
  stroke:var(--accent);stroke-width:2.5;opacity:1;
  stroke-dasharray:8 4;
  animation:dash-flow 1.1s linear infinite;
}
@keyframes dash-flow{to{stroke-dashoffset:-24}}

.pub-list li{position:relative}

/* ===== Dense collapsible Academic Service ===== */
.service{
  border:1px solid var(--rule);
  border-radius:14px;
  background:var(--bg-elev);
  padding:0;margin:0;
  overflow:hidden;
}
.service > summary{
  list-style:none;
  cursor:pointer;
  padding:1rem 1.4rem;
  display:flex;align-items:baseline;justify-content:space-between;gap:1rem;
  font-family:var(--f-serif);
}
.service > summary::-webkit-details-marker{display:none}
.service > summary h2{margin:0;font-size:1.55rem}
.service > summary .hint{
  font-family:var(--f-sans);font-size:.8rem;letter-spacing:.08em;
  color:var(--ink-muted);display:inline-flex;gap:.5rem;align-items:center;
}
.service > summary .hint .caret{
  display:inline-block;transition:transform .25s ease;color:var(--accent);font-size:1rem;
}
.service[open] > summary .hint .caret{transform:rotate(90deg)}

.service-body{padding:0 1.4rem 1.2rem}
.service-group{margin-top:.9rem}
.service-group h4{
  font-family:var(--f-sans);font-size:.72rem;letter-spacing:.18em;
  text-transform:uppercase;color:var(--accent);
  margin:0 0 .5rem;font-weight:600;
}
.svc-row{
  display:grid;
  grid-template-columns:56px 110px 1fr;
  gap:.75rem;align-items:baseline;
  padding:.45rem 0;
  border-top:1px dashed var(--rule);
  font-size:.95rem;
}
.service-group .svc-row:first-of-type{border-top:0}
.svc-tier{
  font-family:var(--f-mono);font-size:.72rem;font-weight:600;
  letter-spacing:.06em;
  padding:.1rem .45rem;border-radius:4px;
  background:color-mix(in oklab,var(--navy) 12%,transparent);
  color:var(--navy);text-align:center;justify-self:start;
}
.svc-tier.q1{background:color-mix(in oklab,var(--accent) 20%,transparent);color:var(--accent)}
.svc-role{
  color:var(--ink-muted);font-style:italic;font-size:.92rem;
}
.svc-name{color:var(--ink);font-weight:500}
@media (max-width:600px){
  .svc-row{grid-template-columns:56px 1fr}
  .svc-role{grid-column:2;margin-top:-.2rem;font-size:.82rem}
  .svc-name{grid-column:2}
}

.section-head{
  display:flex;align-items:baseline;justify-content:space-between;gap:1rem;
  margin-bottom:1rem;border-bottom:1px solid var(--rule);padding-bottom:.6rem;
}
.section-head h2{margin:0}
.section-head a{font-family:var(--f-sans);font-size:.85rem}

code,kbd{
  font-family:var(--f-mono);background:var(--code-bg);
  padding:.12em .35em;border-radius:4px;font-size:.88em;
}

.callout{
  padding:1.1rem 1.3rem;border-radius:12px;
  background:var(--bg-elev);border-left:3px solid var(--accent);
  color:var(--ink-muted);
}

/* print-y CV page */
@media print{
  .nav,footer,.theme-toggle,.mobile-toggle{display:none!important}
  body{background:white;color:black}
  a{color:black;border:0}
}