:root{
  --bg:       #ffffff;   /* page background            */
  --ink:      #1d1d1f;   /* main text (Apple near-black)*/
  --muted:    #6e6e73;   /* secondary text             */
  --hairline: #d2d2d7;   /* thin separators / axes     */
  --accent:   #d62728;   /* one warm red = "emissions" */
  --panel:    #f5f5f7;   /* light grey control panels  */

  --maxw: 1400px;

  /* San Francisco on Apple devices, graceful fallback elsewhere */
  --sans: -apple-system, BlinkMacSystemFont, "SF Pro Text", "Helvetica Neue", Arial, sans-serif;
  --display: -apple-system, BlinkMacSystemFont, "SF Pro Display", "Helvetica Neue", Arial, sans-serif;
}

*{ box-sizing: border-box; }
html{ scroll-behavior: smooth; }

body{
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font-family: var(--sans);
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
}

sub{ font-size: .7em; }

a{ color: var(--accent); text-decoration: none; }
a:hover{ text-decoration: underline; }

/* ============================ INTRO ============================ */
.intro{
  min-height: 100vh;
  display: flex; align-items: center; justify-content: center;
  text-align: center; padding: 2rem;
}
.intro-inner{ max-width: 760px; }

.kicker{
  text-transform: uppercase; letter-spacing: .18em;
  font-size: .8rem; color: var(--muted); margin: 0 0 1.5rem;
}
.intro h1{
  font-family: var(--display);
  font-weight: 600;                       /* Apple uses semibold, not black */
  letter-spacing: -0.02em;
  font-size: clamp(2.6rem, 8vw, 5.5rem);
  line-height: 1.05; margin: 0;
}
.intro h1 .accent{ color: var(--accent); }

.lede{
  font-size: clamp(1.05rem, 2.2vw, 1.35rem);
  color: var(--muted); margin: 1.8rem auto 0; max-width: 600px;
}
/* the small course/group credit line above the title - keep it on one line */
.lede.credit{
  font-size: 1rem; max-width: none; white-space: nowrap; margin-top: .5rem;
}
.scroll-hint{
  margin-top: 3rem; color: var(--muted); font-size: .9rem; letter-spacing: .08em;
  animation: bob 2s ease-in-out infinite;
}
@keyframes bob{ 0%,100%{ transform: translateY(0);} 50%{ transform: translateY(7px);} }

/* ====================== SCROLLYTELLING LAYOUT ======================
   ".view" = two columns: sticky ".graphic" + scrolling ".steps". */
.view{
  position: relative; max-width: var(--maxw); margin: 0 auto; padding: 0 0.5rem;
  display: grid; grid-template-columns: 1.35fr 1fr; gap: 2rem;
}
.graphic{
  position: sticky; top: 0; height: 100vh;
  display: flex; flex-direction: column; align-items: center; justify-content: center;
  background: var(--bg); z-index: 1;
}
.chart{ width: 100%; height: 80vh; }
.graphic:has(.controls) .chart{ height: 66vh; }
#v2 { grid-template-columns: 2.5fr 1fr; }
#v2-chart { height: auto; }
#v2-chart svg { height: auto; }
.chart svg{ width: 100%; height: 100%; overflow: visible; }

.steps{ padding: 16vh 0; }
.step{
  min-height: 60vh;
  display: flex; flex-direction: column; justify-content: center;
  opacity: .35;                              /* inactive steps fade back */
  transition: opacity .35s ease;
}
.step.is-active{ opacity: 1; }
.step h2{
  font-family: var(--display); font-weight: 600; letter-spacing: -0.01em;
  font-size: clamp(1.5rem, 3vw, 2.2rem); line-height: 1.12; margin: 0 0 1rem;
}
.step p{ font-size: 1.1rem; color: var(--muted); margin: .2rem 0; }
.step.is-active p{ color: var(--ink); }
.step strong{ color: var(--ink); font-weight: 600; }
.hl-coal{ color: var(--accent); font-weight: 600; }

/* small control panels (slider / dropdown) under a chart */
.controls{
  margin-top: 1.1rem; display: flex; align-items: center; gap: .7rem;
  background: var(--panel); border-radius: 12px; padding: .55rem 1rem;
  font-size: .9rem; color: var(--muted);
}
.controls label{ white-space: nowrap; }
.controls #v2-year-label{ color: var(--ink); font-weight: 600; font-variant-numeric: tabular-nums; }
.controls input[type=range]{ width: 220px; accent-color: var(--accent); }
.controls select{
  background: #fff; color: var(--ink); border: 1px solid var(--hairline);
  border-radius: 8px; padding: .35rem .6rem; font-family: var(--sans); font-size: .95rem;
}

/* ============================ OUTRO ============================ */
.outro{ max-width: 720px; margin: 0 auto; padding: 20vh 1.5rem 24vh; text-align: center; }
.outro h2{ font-family: var(--display); font-weight: 600; font-size: clamp(1.9rem,5vw,2.8rem); margin: 0 0 1.4rem; }
.outro p{ font-size: 1.15rem; color: var(--muted); }
.outro .source{ font-size: .9rem; margin-top: 2.5rem; }

/* ============================ CHART BITS ============================
   Axes and labels styled via classes, so the JS stays clean. */
.axis text{ fill: var(--muted); font-size: 11px; }
.axis line, .axis path{ stroke: var(--hairline); }
.grid line{ stroke: var(--hairline); stroke-opacity: .6; }
.grid path{ stroke: none; }
.chart-title{ fill: var(--ink); font-size: 13px; font-weight: 600; }
.annotation{ fill: var(--muted); font-size: 12px; }
.annotation.lead{ fill: var(--accent); font-weight: 600; }
.legend text{ fill: var(--muted); font-size: 11px; }

/* faded vs. highlighted shapes (used by treemap / bar steps) */
.faded{ opacity: .2; transition: opacity .4s; }

/* ============================ TOOLTIP ============================ */
.tooltip{
  position: fixed; pointer-events: none; z-index: 50; opacity: 0;
  background: #fff; border: 1px solid var(--hairline); border-radius: 10px;
  padding: .5rem .7rem; font-size: .85rem; color: var(--ink);
  box-shadow: 0 6px 20px rgba(0,0,0,.12); transition: opacity .12s; max-width: 240px;
}
.tooltip .tt-title{ font-weight: 600; margin-bottom: .15rem; }
.tooltip .tt-val{ color: var(--accent); font-variant-numeric: tabular-nums; }

/* ======================= SCROLL PROGRESS RAIL =======================
   Fixed on the right edge: a fill that grows with scroll + one dot per view. */
#progress{
  position: fixed; top: 50%; right: 1.6rem; transform: translateY(-50%);
  z-index: 40; display: flex; flex-direction: column; align-items: center;
  gap: 1.4rem; padding: .4rem 0;
}
.progress-track{
  /* span centre-of-first-dot to centre-of-last-dot (.4rem padding + half a dot) */
  position: absolute; top: calc(.4rem + 5.5px); bottom: calc(.4rem + 5.5px); width: 2px;
  background: var(--hairline); border-radius: 2px; overflow: hidden;
}
.progress-fill{
  position: absolute; top: 0; left: 0; width: 100%; height: 0;
  background: var(--accent); transition: height .15s linear;
}
.progress-dot{
  position: relative; width: 11px; height: 11px; border-radius: 50%;
  background: var(--bg); border: 2px solid var(--hairline);
  box-sizing: border-box; cursor: pointer;
  transition: transform .2s, border-color .2s, background .2s;
}
.progress-dot:hover{ border-color: var(--muted); }
/* every checkpoint reached so far is filled red */
.progress-dot.is-passed{ background: var(--accent); border-color: var(--accent); }
/* the current checkpoint is also enlarged */
.progress-dot.is-active{
  background: var(--accent); border-color: var(--accent); transform: scale(1.35);
}
/* the label sits to the left of its dot and only shows on hover/active */
.progress-label{
  position: absolute; right: 1.6rem; top: 50%; transform: translateY(-50%);
  white-space: nowrap; font-size: .8rem; color: var(--ink);
  background: var(--bg); padding: .15rem .5rem; border-radius: 6px;
  box-shadow: 0 2px 10px rgba(0,0,0,.10);
  opacity: 0; pointer-events: none; transition: opacity .2s;
}
.progress-dot:hover .progress-label,
.progress-dot.is-active .progress-label{ opacity: 1; }

/* ============================ RESPONSIVE ============================ */
@media (min-width: 1101px) and (max-width: 1480px){
  #story{ padding-right: 3rem; }
}
@media (max-width: 1100px){
  .view{ grid-template-columns: 1fr; }
  #v2{ grid-template-columns: 1fr; }
  .graphic{ height: 60vh; top: 8vh; }
  .chart{ height: 50vh; }
  .steps{ padding: 4vh 0; }
  .step{ min-height: auto; padding: 30vh 0; opacity: 1; }
  #progress{ display: none; }   /* hide the rail on narrow screens */
  .lede.credit{ white-space: normal; }  /* let the credit wrap on phones */
}