/* =========================================================
   Nikita Savin — personal site
   Design system: monochrome, IBM Plex Sans
   (palette + type matched to snsoroka.com).
   Token-driven; no arbitrary values outside this block.
   ========================================================= */

:root {
  /* ---- Color · Light (default) ---- */
  --bg:           #fafafa;   /* near-white page              */
  --bg-alt:       #f0f0f0;   /* grouped sections             */
  --surface:      #ffffff;   /* image well / inset           */
  --ink:          #000000;   /* black text                   */
  --ink-soft:     #454545;   /* secondary text               */
  --ink-faint:    #767676;   /* labels, meta, numerals       */
  --accent:       #1a1a1a;   /* near-black interactive       */
  --accent-strong:#000000;   /* hover / pressed              */
  --line:         #dcdcdc;   /* hairline                     */
  --line-strong:  #c4c4c4;   /* hairline on hover            */
  --on-accent:    #fafafa;   /* text on dark fill            */

  /* ---- Dark header (over light body) ---- */
  --nav-bg:       #111111;
  --nav-ink:      #f5f5f5;
  --nav-ink-soft: #a3a3a3;

  /* ---- Type · IBM Plex Sans throughout (matched to snsoroka.com) ---- */
  --font-sans:  "IBM Plex Sans", -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  --font-serif: "IBM Plex Sans", -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;

  --t-label: .75rem;                       /* uppercase labels  */
  --t-meta:  .85rem;                       /* meta, footnotes   */
  --t-body:  1.0625rem;                    /* 17px body         */
  --t-lede:  clamp(1.2rem, 2.1vw, 1.5rem); /* hero lede         */
  --t-h3:    1.3rem;                       /* card / paper title*/
  --t-h2:    clamp(1.7rem, 3.2vw, 2.25rem);
  --t-name:  clamp(2.75rem, 6vw, 4.25rem);

  /* ---- Space (8-pt) ---- */
  --s-1: .5rem;
  --s-2: .75rem;
  --s-3: 1rem;
  --s-4: 1.5rem;
  --s-5: 2rem;
  --s-6: 3rem;
  --s-7: 4.5rem;

  --radius: 3px;
  --maxw: 1060px;
  --pad: clamp(1.5rem, 5vw, 4rem);
  --nav-h: 60px;
  --ease: cubic-bezier(.2, .6, .2, 1);
}

/* ===== Base ===== */
* { box-sizing: border-box; }

html {
  scroll-behavior: smooth;
  scroll-padding-top: calc(var(--nav-h) + var(--s-4));
  -webkit-text-size-adjust: 100%;
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font-family: var(--font-sans);
  font-size: var(--t-body);
  line-height: 1.7;
  font-feature-settings: "kern", "liga";
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}

img { max-width: 100%; display: block; }

a {
  color: var(--accent);
  text-decoration: none;
  transition: color .2s var(--ease);
}
a:hover {
  color: var(--accent-strong);
  text-decoration: underline;
  text-underline-offset: .2em;
  text-decoration-thickness: 1px;
}

h1, h2, h3 {
  font-family: var(--font-serif);
  font-weight: 400;            /* regular, matched to snsoroka.com */
  line-height: 1.2;
  letter-spacing: -.04em;      /* tight tracking, matched to snsoroka.com */
  color: var(--ink);
}

::selection { background: var(--accent); color: var(--on-accent); }

/* shared content container */
.section__head,
.papers,
.pubs,
.contact {
  max-width: var(--maxw);
  margin-inline: auto;
  padding-inline: var(--pad);
}

/* ===== Navigation ===== */
.nav {
  position: sticky;
  top: 0;
  z-index: 50;
  background: var(--nav-bg);
}
.nav__inner {
  max-width: var(--maxw);
  margin-inline: auto;
  padding: var(--s-3) var(--pad);
  min-height: var(--nav-h);
  display: flex;
  align-items: center;
  gap: var(--s-5);
}
.nav__brand {
  font-family: var(--font-serif);
  font-weight: 500;
  font-size: 1rem;
  letter-spacing: .04em;
  text-transform: uppercase;
  color: var(--nav-ink);
}
.nav__brand:hover { color: var(--nav-ink); text-decoration: none; }

.nav__links {
  margin-left: auto;
  display: flex;
  gap: var(--s-4);
  font-size: .9rem;
}
.nav__links a {
  position: relative;
  color: var(--nav-ink-soft);
  font-weight: 500;
  padding-block: .2rem;
}
.nav__links a:hover { color: var(--nav-ink); text-decoration: none; }
.nav__links a.is-active { color: var(--nav-ink); }
.nav__links a.is-active::after {
  content: "";
  position: absolute;
  left: 0; right: 0; bottom: -1px;
  height: 1px;
  background: var(--nav-ink);
}

/* ===== Hero ===== */
.hero {
  max-width: var(--maxw);
  margin-inline: auto;
  padding: clamp(4rem, 9vw, 7rem) var(--pad) clamp(3rem, 6vw, 5rem);
}
.hero__grid {
  display: grid;
  grid-template-columns: 1.7fr 1fr;
  gap: clamp(2.5rem, 5vw, 5rem);
  align-items: center;
}
.eyebrow {
  margin: 0 0 var(--s-4);
  font-size: var(--t-label);
  font-weight: 600;
  letter-spacing: .18em;
  text-transform: uppercase;
  color: var(--ink-faint);
}
.hero__name {
  margin: 0 0 var(--s-4);
  font-family: var(--font-serif);
  font-weight: 400;
  font-size: var(--t-name);
  letter-spacing: -.01em;      /* slightly looser than body headings for caps */
  text-transform: uppercase;
}
.hero__intro {
  margin: 0 0 var(--s-4);
  max-width: 54ch;
  font-size: 1.125rem;
  line-height: 1.6;
  color: var(--ink);
}
.hero__intro:last-of-type { margin-bottom: var(--s-5); }

/* ---- Buttons ---- */
.hero__links { display: flex; flex-wrap: wrap; gap: var(--s-2); }
.btn {
  display: inline-flex;
  align-items: center;
  padding: .6rem 1.05rem;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: transparent;
  color: var(--ink);
  font-size: .9rem;
  font-weight: 500;
  transition: border-color .2s var(--ease), color .2s var(--ease), background .2s var(--ease);
}
.btn:hover {
  border-color: var(--ink);
  color: var(--ink);
  text-decoration: none;
}
.btn--primary {
  border-color: var(--accent);
  background: var(--accent);
  color: var(--on-accent);
}
.btn--primary:hover {
  border-color: var(--accent-strong);
  background: var(--accent-strong);
  color: var(--on-accent);
}

/* ---- Portrait + facts ---- */
.portrait {
  aspect-ratio: 4 / 5;
  overflow: hidden;
  border-radius: var(--radius);
  background: linear-gradient(160deg, var(--accent), var(--accent-strong));
  display: grid;
  place-items: center;
}
.portrait img {
  width: 100%; height: 100%;
  object-fit: cover;
  object-position: center 20%;
}
.portrait__initials {
  font-family: var(--font-serif);
  font-size: 3rem;
  color: var(--on-accent);
}

.facts { margin: var(--s-4) 0 0; }
.facts div {
  display: grid;
  gap: .15rem;
  padding: var(--s-3) 0;
  border-bottom: 1px solid var(--line);
}
.facts div:first-child { border-top: 1px solid var(--line); }
.facts dt {
  font-size: var(--t-label);
  font-weight: 600;
  letter-spacing: .14em;
  text-transform: uppercase;
  color: var(--ink-faint);
}
.facts dd { margin: 0; color: var(--ink); }

/* ===== Sections ===== */
.section {
  padding: clamp(3.5rem, 7vw, 6rem) 0;
  border-top: 1px solid var(--line);
}
.section--alt { background: var(--bg-alt); }

.section__head { margin-bottom: var(--s-6); }
.section__head h2 { margin: 0 0 var(--s-2); font-size: var(--t-h2); }
.section__note {
  margin: 0;
  max-width: 60ch;
  color: var(--ink-soft);
  font-size: .95rem;
}

/* ---- Research (numbered, ruled) ---- */
.papers { list-style: none; margin: 0; counter-reset: paper; }
.paper {
  counter-increment: paper;
  display: grid;
  grid-template-columns: 3rem 1fr;
  column-gap: var(--s-4);
  row-gap: 0;
  padding: var(--s-5) 0;
  border-top: 1px solid var(--line);
}
.paper:first-child { border-top: none; padding-top: 0; }
.paper::before {
  content: counter(paper, decimal-leading-zero);
  grid-column: 1;
  grid-row: 1;
  padding-top: .35rem;
  font-size: var(--t-meta);
  font-weight: 600;
  letter-spacing: .08em;
  color: var(--ink-faint);
}
.paper__title,
.paper__meta,
.paper__abstract { grid-column: 2; }
.paper__title {
  margin: 0 0 var(--s-2);
  font-size: var(--t-h3);
  font-weight: 400;
  line-height: 1.25;
}
.paper__meta {
  margin: 0 0 var(--s-2);
  font-size: var(--t-meta);
  color: var(--ink-faint);
}
.paper__abstract {
  margin: 0;
  max-width: 68ch;
  color: var(--ink-soft);
}

/* ---- Publications ---- */
.pubs__group {
  margin: var(--s-6) 0 var(--s-4);
  padding-bottom: var(--s-2);
  border-bottom: 1px solid var(--line);
  font-family: var(--font-sans);
  font-size: var(--t-label);
  font-weight: 600;
  letter-spacing: .16em;
  text-transform: uppercase;
  color: var(--ink-faint);
}
.pubs__group:first-child { margin-top: 0; }
.pub-list { list-style: none; margin: 0; padding: 0; display: grid; gap: var(--s-4); }
.pub-list li { max-width: 76ch; line-height: 1.6; color: var(--ink-soft); }
.pub-title  { color: var(--ink); font-weight: 500; }
.pub-venue  { font-style: italic; color: var(--ink); }
.pub-with   { color: var(--ink-faint); }
.pub-link   { color: var(--ink); }
.pub-link:hover { color: var(--accent-strong); }
.ext-arrow  {
  display: inline-block;
  margin-left: .2em;
  font-size: .8em;
  color: var(--ink-faint);
  text-decoration: none;
  vertical-align: .08em;
}
.pubs__note {
  margin: var(--s-5) 0 0;
  max-width: 72ch;
  color: var(--ink-soft);
  font-size: .95rem;
}

/* ---- Teaching (ruled table) ---- */
.teaching { list-style: none; margin: 0; padding: 0; }
.teaching li {
  display: flex;
  justify-content: space-between;
  align-items: baseline;
  gap: var(--s-4);
  padding: var(--s-3) 0;
  border-bottom: 1px solid var(--line);
}
.teaching li > :first-child { flex: 1 1 0; min-width: 0; }   /* title wraps internally */
.teaching strong { font-weight: 500; color: var(--ink); }
.teaching li > span:last-child {                              /* venue/date stays right */
  flex: 0 0 auto;
  white-space: nowrap;
  font-size: var(--t-meta);
  color: var(--ink-faint);
}
.wri-with {                                                   /* co-author, right after title */
  margin-left: .3em;
  font-size: var(--t-meta);
  color: var(--ink-faint);
}
@media (max-width: 620px) {
  .teaching li { flex-direction: column; align-items: flex-start; gap: 2px; }
  .teaching li > span:last-child { white-space: normal; }
}

/* Student comments */
.quotes {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: var(--s-5) var(--s-6);
  margin-top: var(--s-2);
}
.quote { margin: 0; }
.quote p {
  margin: 0 0 var(--s-3);
  line-height: 1.6;
  color: var(--ink);
}
.quote cite {
  font-style: normal;
  font-size: var(--t-label);
  font-weight: 600;
  letter-spacing: .1em;
  text-transform: uppercase;
  color: var(--ink-faint);
}
@media (max-width: 800px) {
  .quotes { grid-template-columns: 1fr; gap: var(--s-5); }
}

/* ---- Contact ---- */
.contact { max-width: 56ch; }
.contact h2 { margin: 0 0 var(--s-3); font-size: var(--t-h2); }
.contact p  { margin: 0 0 var(--s-5); color: var(--ink-soft); }

/* ---- Footer ---- */
.footer { border-top: 1px solid var(--line); }
.footer__inner {
  max-width: var(--maxw);
  margin-inline: auto;
  padding: var(--s-5) var(--pad);
  display: flex;
  justify-content: space-between;
  align-items: center;
  font-size: var(--t-meta);
  color: var(--ink-faint);
}
.footer__inner a { color: var(--ink-faint); }
.footer__inner a:hover { color: var(--ink); }

/* ===== Motion: a single, subtle reveal (JS-gated) ===== */
.js .reveal {
  opacity: 0;
  transform: translateY(12px);
  transition: opacity .7s var(--ease), transform .7s var(--ease);
}
.js .reveal.is-visible { opacity: 1; transform: none; }

/* ===== Responsive ===== */
@media (max-width: 800px) {
  .hero__grid { grid-template-columns: 1fr; }
  .hero__card { max-width: 360px; }

  .nav__inner { flex-wrap: wrap; gap: var(--s-3); }
  .nav__links {
    order: 3;
    width: 100%;
    margin-left: 0;
    overflow-x: auto;
    gap: var(--s-4);
    padding-bottom: 2px;
    scrollbar-width: none;
  }
  .nav__links::-webkit-scrollbar { display: none; }

  .paper { grid-template-columns: 1fr; row-gap: var(--s-2); }
  .paper::before,
  .paper__title,
  .paper__meta,
  .paper__abstract { grid-column: 1; }
  .paper::before { grid-row: auto; padding-top: 0; }
}

@media (prefers-reduced-motion: reduce) {
  * { transition: none !important; scroll-behavior: auto !important; }
  .js .reveal { opacity: 1; transform: none; }
}