/* ============================================================
   Becoming an AI Researcher — phd-in-ai.com
   Palette sampled from the book cover (Cambridge University Press)
   ============================================================ */

:root{
  /* Surfaces */
  --bg:            #dbebe9;   /* cover ground, mint */
  --bg-alt:        #eef6f5;
  --surface:       #ffffff;
  --border:        rgba(18, 65, 75, .14);
  --border-strong: rgba(18, 65, 75, .26);

  /* Type */
  --ink:           #12414b;   /* cover title ink */
  --text:          #1d4f59;
  --text-muted:    #47707a;
  --text-dim:      #46686f;

  /* Accents */
  --green:         #3f6b3c;   /* links, CTA */
  --green-deep:    #345a32;
  --green-soft:    #548251;   /* cover green */
  --blue:          #4b707c;   /* cover node blue */
  --sage:          #a2c2a7;

  /* Type scale */
  --font-sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Helvetica, Arial, "Noto Sans", sans-serif;
  --font-mono: ui-monospace, SFMono-Regular, "SF Mono", Menlo, Consolas, "Liberation Mono", monospace;

  /* Layout */
  --wrap: 1120px;
  --radius: 6px;
  --radius-sm: 6px;
  --header-h: 64px;
}

/* ---------- Reset ---------- */
*, *::before, *::after{ box-sizing: border-box; }

html{
  scroll-behavior: smooth;
  scroll-padding-top: calc(var(--header-h) + 16px);
  -webkit-text-size-adjust: 100%;
}

body{
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: var(--font-sans);
  font-size: 17px;
  line-height: 1.68;
  letter-spacing: .005em;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  overflow-x: hidden;
}

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

h1, h2, h3{
  line-height: 1.18;
  letter-spacing: -.02em;
  margin: 0 0 .6em;
  font-weight: 650;
  color: var(--ink);
}

p{ margin: 0 0 1.1em; }
p:last-child{ margin-bottom: 0; }

a{
  color: var(--green);
  text-decoration: none;
  transition: color .18s ease, border-color .18s ease;
}
a:hover{ color: var(--green-deep); }

.section p a, .site-footer a, .byline a, .section-lede a, .author-text a, .hero-note a{
  border-bottom: 1px solid rgba(63, 107, 60, .34);
  padding-bottom: 1px;
}
.section p a:hover, .site-footer a:hover, .byline a:hover, .author-text a:hover, .hero-note a:hover{
  border-bottom-color: var(--green-deep);
}

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

.wrap{
  width: 100%;
  max-width: var(--wrap);
  margin: 0 auto;
  padding: 0 24px;
}

.skip-link{
  position: absolute;
  left: -9999px;
  top: 0;
  z-index: 200;
  background: var(--green);
  color: #fff;
  padding: 10px 18px;
  border-radius: 0 0 var(--radius-sm) 0;
  font-weight: 600;
}
.skip-link:focus{ left: 0; }

/* ============================================================
   Header
   ============================================================ */
.site-header{
  position: fixed;
  inset: 0 0 auto 0;
  height: var(--header-h);
  z-index: 100;
  background: rgba(219, 235, 233, .72);
  backdrop-filter: blur(14px) saturate(140%);
  -webkit-backdrop-filter: blur(14px) saturate(140%);
  border-bottom: 1px solid transparent;
  transition: background .25s ease, border-color .25s ease;
}
.site-header.is-scrolled{
  background: rgba(232, 243, 242, .94);
  border-bottom-color: var(--border);
}

.header-inner{
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 24px;
}

.brand{
  display: inline-flex;
  align-items: center;
  gap: 10px;
  color: var(--ink);
  font-weight: 500;
  font-size: .95rem;
  white-space: nowrap;
}
.brand:hover{ color: var(--ink); }
.brand b{ font-weight: 680; }

.brand-mark{
  width: 22px;
  height: 22px;
  flex: none;
  display: block;
  fill: var(--green-soft);
}
.brand-mark .mark-stem{ stroke: var(--blue); }

.nav ul{
  display: flex;
  align-items: center;
  gap: 2px;
  list-style: none;
  margin: 0;
  padding: 0;
}
.nav a{
  display: block;
  padding: 8px 11px;
  border-radius: 999px;
  color: var(--text-muted);
  font-size: .92rem;
  font-weight: 500;
}
.nav a:hover{ color: var(--ink); background: rgba(18, 65, 75, .07); }
.nav a.is-active{ color: var(--green); background: rgba(84, 130, 81, .14); }

.nav-toggle{
  display: none;
  width: 42px; height: 42px;
  border: 1px solid var(--border-strong);
  border-radius: var(--radius-sm);
  background: transparent;
  cursor: pointer;
  padding: 0;
  place-items: center;
}
.nav-toggle span{
  display: block;
  width: 18px; height: 1.6px;
  background: var(--ink);
  margin: 3.4px auto;
  transition: transform .25s ease, opacity .2s ease;
}
.nav-toggle[aria-expanded="true"] span:nth-child(1){ transform: translateY(5px) rotate(45deg); }
.nav-toggle[aria-expanded="true"] span:nth-child(2){ opacity: 0; }
.nav-toggle[aria-expanded="true"] span:nth-child(3){ transform: translateY(-5px) rotate(-45deg); }

/* ============================================================
   Hero
   ============================================================ */
.hero{
  position: relative;
  padding: calc(var(--header-h) + 76px) 0 92px;
  overflow: hidden;
  background:
    radial-gradient(120% 90% at 80% 6%, rgba(162, 194, 167, .35), transparent 58%),
    radial-gradient(90% 80% at 4% 0%, rgba(122, 168, 180, .20), transparent 62%),
    var(--bg);
}
.hero::after{
  content: "";
  position: absolute;
  inset: auto 0 0 0;
  height: 1px;
  background: linear-gradient(90deg, transparent, var(--border-strong), transparent);
}

.hero-inner{
  position: relative;
  display: grid;
  grid-template-columns: minmax(0, 1.3fr) minmax(0, .7fr);
  gap: 64px;
  align-items: center;
}

.eyebrow{
  display: inline-block;
  margin: 0 0 18px;
  padding: 5px 13px;
  border: 1px solid var(--border-strong);
  border-radius: 999px;
  background: rgba(255, 255, 255, .5);
  color: var(--ink);
  font-size: .74rem;
  font-weight: 600;
  letter-spacing: .12em;
  text-transform: uppercase;
}

.hero h1{
  margin: 0 0 .26em;
  font-size: clamp(2.3rem, 5.8vw, 3.9rem);
  font-weight: 700;
  letter-spacing: -.032em;
  color: var(--ink);
}

.subtitle{
  margin: 0 0 1.1em;
  font-size: clamp(1.05rem, 2.3vw, 1.4rem);
  font-weight: 500;
  color: var(--green-soft);
}

.byline{
  margin: 0 0 1.5em;
  font-size: .98rem;
  color: var(--text-muted);
}

.lede{
  max-width: 46ch;
  font-size: 1.06rem;
  color: var(--text-muted);
  margin-bottom: 2em;
}

.cta-row{
  display: flex;
  flex-wrap: wrap;
  gap: 14px;
}

.btn{
  display: inline-flex;
  flex-direction: column;
  align-items: flex-start;
  gap: 1px;
  padding: 13px 24px;
  border-radius: var(--radius-sm);
  font-size: 1rem;
  font-weight: 600;
  letter-spacing: .005em;
  border: 1px solid transparent;
  transition: transform .18s ease, box-shadow .22s ease, background .2s ease, border-color .2s ease, color .2s ease;
}
.btn:hover{ transform: translateY(-2px); }
.btn-meta{
  font-size: .74rem;
  font-weight: 500;
  letter-spacing: .04em;
  opacity: .78;
}

.btn-primary{
  background: var(--green);
  color: #fff;
  box-shadow: 0 6px 18px -10px rgba(18, 65, 75, .6);
}
.btn-primary:hover{ background: var(--green-deep); color: #fff; }

.btn-ghost{
  background: rgba(255, 255, 255, .62);
  border-color: var(--border-strong);
  color: var(--ink);
}
.btn-ghost:hover{ color: var(--ink); background: #fff; border-color: var(--green-soft); }

.hero-note{
  margin: 20px 0 0;
  font-size: .9rem;
  color: var(--text-muted);
}
.tag{
  display: inline-block;
  margin-right: 8px;
  padding: 2px 9px;
  border-radius: 999px;
  background: rgba(84, 130, 81, .16);
  color: var(--green-deep);
  font-size: .74rem;
  font-weight: 700;
  letter-spacing: .07em;
  text-transform: uppercase;
}

.hero-cover{
  position: relative;
  justify-self: center;
}
.hero-cover img{
  width: min(300px, 100%);
  box-shadow:
    0 26px 50px -26px rgba(18, 65, 75, .55),
    0 0 0 1px rgba(18, 65, 75, .12);
  transform: perspective(1400px) rotateY(-8deg) rotateX(1.5deg);
  transition: transform .5s cubic-bezier(.22,.9,.3,1);
}
.hero-cover img:hover{
  transform: perspective(1400px) rotateY(-3deg) rotateX(0deg) translateY(-4px);
}

/* ============================================================
   Sections
   ============================================================ */
.section{ padding: 88px 0; }
.section-alt{ background: var(--bg-alt); border-block: 1px solid var(--border); }

.section-title{
  position: relative;
  font-size: clamp(1.5rem, 3.2vw, 2.05rem);
  margin-bottom: .8em;
  padding-top: 18px;
}
.section-title::before{
  content: "";
  position: absolute;
  top: 0; left: 0;
  width: 46px; height: 3px;
  border-radius: 3px;
  background: linear-gradient(90deg, var(--green-soft), transparent);
}

.section-lede{
  color: var(--text-muted);
  margin-top: -.4em;
  margin-bottom: 2em;
}

/* ---------- About ---------- */
.about-grid p{ color: var(--text-muted); max-width: 68ch; }

.fact-row{
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 1px;
  list-style: none;
  margin: 48px 0 0;
  padding: 0;
  background: var(--border);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  overflow: hidden;
}
.fact-row li{
  background: var(--surface);
  padding: 22px 24px;
  display: flex;
  flex-direction: column;
  gap: 4px;
}
.fact-key{
  font-size: .71rem;
  letter-spacing: .13em;
  text-transform: uppercase;
  color: var(--text-dim);
}
.fact-val{ font-weight: 600; color: var(--ink); }

/* ---------- Cards ---------- */
.card-grid{ display: grid; gap: 24px; }
.card-grid.two{ grid-template-columns: repeat(2, minmax(0, 1fr)); }

.card{
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 30px 32px;
  transition: border-color .22s ease, transform .22s ease, box-shadow .22s ease;
}
.card:hover{
  border-color: var(--border-strong);
  transform: translateY(-3px);
  box-shadow: 0 18px 34px -26px rgba(18, 65, 75, .5);
}
.card h3{ font-size: 1.14rem; margin-bottom: .7em; }
.card p{ color: var(--text-muted); font-size: .97rem; }

.card-feature{
  background: linear-gradient(160deg, #fff, #eaf4f2);
  display: flex;
  flex-direction: column;
  align-items: flex-start;
}
.card-feature .btn{ margin-top: auto; }

/* ---------- Social ---------- */
.social-row{
  list-style: none;
  margin: 18px 0 0;
  padding: 0;
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
}
.social-row a{
  display: inline-flex;
  align-items: center;
  gap: 9px;
  padding: 8px 14px 8px 10px;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  background: var(--bg-alt);
  color: var(--ink);
  font-size: .92rem;
  font-weight: 550;
  transition: border-color .2s ease, background .2s ease, transform .2s ease;
}
.social-row a:hover{ border-color: var(--green-soft); background: #fff; transform: translateY(-2px); }
.social-row img{ width: 22px; height: 22px; border-radius: 4px; }

/* ---------- Table of contents ---------- */
.toc-grid{
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 12px 48px;
}
.toc-list{
  list-style: none;
  margin: 0;
  padding: 0;
  display: grid;
  gap: 10px;
  align-content: start;
}
.toc-list li{
  display: grid;
  grid-template-columns: 2.4rem 1fr;
  align-items: baseline;
  color: var(--text-muted);
  font-size: .99rem;
}
.ch-num{
  font-family: var(--font-mono);
  font-size: .82rem;
  color: var(--blue);
}

/* ---------- Endorsements ---------- */
.quote-grid{
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
  gap: 24px;
}
.quote{
  position: relative;
  margin: 0;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 30px 32px 26px;
  display: flex;
  flex-direction: column;
  transition: border-color .22s ease, transform .22s ease;
}
.quote:hover{ border-color: var(--border-strong); transform: translateY(-3px); }
.quote::before{
  content: "\201C";
  position: absolute;
  top: 6px; right: 22px;
  font-size: 4.4rem;
  line-height: 1;
  color: var(--sage);
  opacity: .55;
}
.quote blockquote{
  margin: 0 0 22px;
  color: var(--text);
  font-size: .99rem;
  line-height: 1.62;
}
.quote blockquote::before{ content: "\201C"; }
.quote blockquote::after{ content: "\201D"; }
.quote figcaption{
  margin-top: auto;
  padding-top: 16px;
  border-top: 1px solid var(--border);
  display: flex;
  flex-direction: column;
  gap: 3px;
}
.q-name{ font-weight: 680; color: var(--green); font-size: .95rem; }
.q-aff{ color: var(--text-dim); font-size: .84rem; line-height: 1.45; }

/* ---------- Author ---------- */
.author-grid{
  display: grid;
  grid-template-columns: minmax(0, 1fr) 260px;
  gap: 48px;
  align-items: start;
}
.author-text{ color: var(--text-muted); }

.author-photo{
  margin: 0;
  justify-self: end;
}
.author-photo img{
  width: 260px;
  border-radius: var(--radius);
  box-shadow:
    0 18px 34px -24px rgba(18, 65, 75, .55),
    0 0 0 1px rgba(18, 65, 75, .12);
}

/* ---------- Citation ---------- */
.citation-plain{
  color: var(--text-muted);
  max-width: 72ch;
  margin-bottom: 1.8em;
}

.code-block{
  margin: 0;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  overflow: hidden;
  background: var(--surface);
}
.code-block figcaption{
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 11px 18px;
  background: var(--bg-alt);
  border-bottom: 1px solid var(--border);
  font-size: .75rem;
  letter-spacing: .13em;
  text-transform: uppercase;
  color: var(--text-dim);
}
.code-block pre{
  margin: 0;
  padding: 22px 24px;
  overflow-x: auto;
  font-family: var(--font-mono);
  font-size: .85rem;
  line-height: 1.65;
  color: var(--ink);
}

.copy-btn{
  font: inherit;
  font-size: .72rem;
  letter-spacing: .1em;
  text-transform: uppercase;
  color: var(--green);
  background: rgba(84, 130, 81, .12);
  border: 1px solid var(--border-strong);
  border-radius: var(--radius-sm);
  padding: 5px 12px;
  cursor: pointer;
  transition: background .18s ease, color .18s ease;
}
.copy-btn:hover{ background: rgba(84, 130, 81, .22); }
.copy-btn.is-copied{ color: #2c6b46; border-color: rgba(44, 107, 70, .45); background: rgba(44, 107, 70, .14); }

/* ---------- Closing ---------- */
.closing{
  padding: 92px 0;
  background:
    radial-gradient(90% 140% at 50% 0%, rgba(162, 194, 167, .38), transparent 62%),
    var(--bg);
  border-top: 1px solid var(--border);
  text-align: center;
}
.closing-inner h2{ font-size: clamp(1.6rem, 3.4vw, 2.2rem); }
.closing-inner p{ color: var(--text-muted); margin-bottom: 2em; }
.closing .cta-row{ justify-content: center; }
.closing .btn{ align-items: center; }

/* ---------- Footer ---------- */
.site-footer{
  background: var(--bg);
  border-top: 1px solid var(--border);
  padding: 34px 0;
  color: var(--text-dim);
  font-size: .88rem;
}
.footer-inner{
  display: flex;
  flex-wrap: wrap;
  gap: 8px 28px;
  justify-content: space-between;
}
.site-footer p{ margin: 0; }
.site-footer a{ color: var(--text-muted); }
.site-footer a:hover{ color: var(--green); }

/* ============================================================
   Responsive
   ============================================================ */
@media (max-width: 1040px){
  .brand-text{ display: none; }
}

@media (max-width: 980px){
  .hero-inner{ grid-template-columns: 1fr; gap: 44px; }
  .hero-cover{ order: -1; justify-self: start; }
  .hero-cover img{ width: min(200px, 52vw); transform: none; }
  .hero-cover img:hover{ transform: translateY(-4px); }
  .toc-grid{ grid-template-columns: 1fr; }
  .author-grid{ grid-template-columns: 1fr; gap: 28px; }
  .author-photo{ justify-self: start; order: -1; }
  .author-photo img{ width: min(200px, 50vw); }
}

@media (max-width: 760px){
  body{ font-size: 16px; }
  .wrap{ padding: 0 20px; }
  .section{ padding: 64px 0; }
  .hero{ padding: calc(var(--header-h) + 48px) 0 68px; }

  .brand-text{ display: inline; }
  .nav-toggle{ display: grid; }
  .nav{
    position: fixed;
    inset: var(--header-h) 0 auto 0;
    background: rgba(232, 243, 242, .98);
    backdrop-filter: blur(14px);
    -webkit-backdrop-filter: blur(14px);
    border-bottom: 1px solid var(--border);
    transform: translateY(-8px);
    opacity: 0;
    visibility: hidden;
    transition: opacity .2s ease, transform .2s ease, visibility .2s;
  }
  .nav.is-open{ opacity: 1; visibility: visible; transform: translateY(0); }
  .nav ul{
    flex-direction: column;
    align-items: stretch;
    gap: 0;
    padding: 10px 12px 18px;
  }
  .nav a{ padding: 13px 14px; border-radius: var(--radius-sm); font-size: 1rem; }

  .card-grid.two{ grid-template-columns: 1fr; }
  .card, .quote{ padding: 24px 22px; }
  .quote-grid{ grid-template-columns: 1fr; }
  .btn{ width: 100%; align-items: center; }
  .footer-inner{ flex-direction: column; }
}

/* ---------- Motion & print ---------- */
@media (prefers-reduced-motion: reduce){
  html{ scroll-behavior: auto; }
  *, *::before, *::after{
    animation-duration: .001ms !important;
    transition-duration: .001ms !important;
  }
  .btn:hover, .card:hover, .quote:hover, .hero-cover img:hover, .social-row a:hover{ transform: none; }
}

@media print{
  .site-header, .closing, .nav-toggle, .copy-btn{ display: none !important; }
  body{ background: #fff; color: #000; }
  a{ color: #000; }
}