/* "What is a tachyon?" (tachyon.html). Builds on styles.css tokens and components.
   Reading levels: the radio group in .levels picks which .lv-* blocks show. CSS :has() does the
   switching, so it works without JavaScript; tachyon.js adds saving, ?level= and keeping your
   place. Without :has() support, only Standard shows (the default below). */

/* Levels: Standard unless a level radio says otherwise. */
.lv { display: none; }
.lv-standard { display: block; }
span.lv-standard { display: inline; }
.levels-hint span { display: none; }
.levels-hint .for-standard { display: inline; }

body:has(.levels input[value="eli5"]:checked) .lv-standard,
body:has(.levels input[value="eli13"]:checked) .lv-standard,
body:has(.levels input[value="phd"]:checked) .lv-standard,
body:has(.levels input[value="eli5"]:checked) .for-standard,
body:has(.levels input[value="eli13"]:checked) .for-standard,
body:has(.levels input[value="phd"]:checked) .for-standard { display: none; }

body:has(.levels input[value="eli5"]:checked) div.lv-eli5,
body:has(.levels input[value="eli5"]:checked) p.lv-eli5,
body:has(.levels input[value="eli13"]:checked) div.lv-eli13,
body:has(.levels input[value="eli13"]:checked) p.lv-eli13,
body:has(.levels input[value="phd"]:checked) div.lv-phd,
body:has(.levels input[value="phd"]:checked) p.lv-phd { display: block; }
body:has(.levels input[value="eli5"]:checked) span.lv-eli5,
body:has(.levels input[value="eli13"]:checked) span.lv-eli13,
body:has(.levels input[value="phd"]:checked) span.lv-phd,
body:has(.levels input[value="eli5"]:checked) .for-eli5,
body:has(.levels input[value="eli13"]:checked) .for-eli13,
body:has(.levels input[value="phd"]:checked) .for-phd { display: inline; }

/* Shared by every level except ELI5. */
body:has(.levels input[value="eli5"]:checked) .lv-notkid { display: none; }

/* The level switch: a sticky segmented control under the site header. */
.levels {
  position: sticky;
  top: 68px;
  z-index: 15;
  background: var(--header-bg);
  backdrop-filter: saturate(180%) blur(8px);
  -webkit-backdrop-filter: saturate(180%) blur(8px);
  border-bottom: 1px solid var(--border-subtle);
}

.levels-inner {
  display: flex;
  align-items: center;
  gap: 16px;
  min-height: 56px;
  flex-wrap: wrap;
}

.levels fieldset {
  display: flex;
  align-items: center;
  gap: 12px;
  margin: 0;
  padding: 0;
  border: 0;
  min-width: 0;
}

.levels legend {
  float: left;
  padding: 0;
  font-size: 12px;
  font-weight: 600;
  letter-spacing: 0.16em;
  text-transform: uppercase;
  color: var(--text-muted);
}

.levels-options {
  display: inline-flex;
  padding: 3px;
  gap: 2px;
  border-radius: 999px;
  background: var(--surface-sunken);
  border: 1px solid var(--border-subtle);
}

.levels-options label { position: relative; }

.levels-options input {
  position: absolute;
  opacity: 0;
  inset: 0;
  margin: 0;
  cursor: pointer;
}

.levels-options span {
  display: inline-flex;
  align-items: center;
  height: 32px;
  padding: 0 14px;
  border-radius: 999px;
  font-size: 14px;
  font-weight: 600;
  color: var(--text-body);
  white-space: nowrap;
  transition: background var(--dur-fast) var(--ease-out), color var(--dur-fast);
}

.levels-options label:hover span { color: var(--text-strong); }

.levels-options input:checked + span {
  background: var(--surface-card);
  color: var(--pill-text);
  box-shadow: var(--shadow-sm);
}

.levels-options input:focus-visible + span {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

.levels-hint {
  margin: 0;
  font-size: 14px;
  color: var(--text-muted);
}

/* Anchor targets clear both sticky bars. */
html:has(body.explainer) { scroll-padding-top: 140px; }

/* Article */
.explainer-body {
  max-width: 760px;
  padding-top: 56px;
  padding-bottom: 96px;
}

.explainer-head h1 {
  margin: 16px 0;
  font-size: clamp(38px, 6vw, 60px);
  letter-spacing: -0.02em;
}

.explainer-lead {
  margin: 0 0 24px;
  font-size: 20px;
  line-height: 1.55;
  color: var(--text-strong);
}

.feinberg {
  margin: 32px 0 8px;
  padding: 0 0 0 20px;
  border-left: 3px solid var(--accent);
}

.feinberg p {
  margin: 0 0 6px;
  font-size: 22px;
  line-height: 1.4;
  font-weight: 600;
  color: var(--text-strong);
}

.feinberg footer {
  font-size: 14px;
  color: var(--text-muted);
}

.explainer-body section { margin-top: 72px; }

.explainer-body h2 {
  display: flex;
  align-items: baseline;
  gap: 12px;
  margin: 0 0 16px;
  font-size: clamp(26px, 3.2vw, 34px);
  line-height: 1.2;
}

.sec-num {
  flex: none;
  font-size: 14px;
  font-weight: 600;
  color: var(--pill-text);
  background: var(--accent-soft);
  border-radius: 999px;
  min-width: 28px;
  height: 28px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  transform: translateY(-4px);
}

.explainer-body p,
.explainer-body li,
.explainer-body dd {
  color: var(--text-body);
  font-size: 17px;
  line-height: 1.7;
}

.explainer-body p { margin: 0 0 16px; }

/* Not buttons: this selector outranks .btn-primary and turned its white label blue on blue. */
.explainer-body a:not(.btn) { color: var(--text-link); }
.explainer-body a:not(.btn):hover { color: var(--text-link-hover); }

.honest {
  padding: 14px 16px;
  border-radius: var(--radius-md);
  background: var(--surface-sunken);
  border: 1px solid var(--border-subtle);
  font-size: 15px !important;
}

.honest strong { color: var(--text-strong); }

.numbers { margin: 0 0 16px; padding-left: 20px; }

.eq {
  margin: 20px 0 !important;
  padding: 14px 18px;
  overflow-x: auto;
  border-radius: var(--radius-md);
  background: var(--surface-sunken);
  font-family: var(--font-mono);
  font-size: 15px !important;
  color: var(--text-strong) !important;
  white-space: nowrap;
}

/* Visualizations */
.viz {
  margin: 32px 0 8px;
  padding: 20px;
  border-radius: var(--radius-lg);
  background: var(--surface-card);
  border: 1px solid var(--border-subtle);
  box-shadow: var(--shadow-sm);
}

.viz-stage { position: relative; }

.viz-svg {
  display: block;
  width: 100%;
  height: auto;
  overflow: visible;
  touch-action: none;
  font-family: var(--font-sans);
  user-select: none;
  -webkit-user-select: none;
}

.viz-svg text { fill: var(--text-muted); font-size: 13px; }
.viz-svg .t-strong { fill: var(--text-strong); font-weight: 600; }
.viz-svg .t-accent { fill: var(--pill-text); font-weight: 600; }
.viz-svg .t-violet { fill: var(--violet-text); font-weight: 600; }
.viz-svg .t-warn { fill: var(--warn-text); font-weight: 600; }
.viz-svg .grid { stroke: var(--border-subtle); stroke-width: 1; }
.viz-svg .axis { stroke: var(--border-default); stroke-width: 1.5; }
.viz-svg .light { stroke: var(--viz-light); stroke-width: 2; stroke-dasharray: 2 6; stroke-linecap: round; }
.viz-svg .cone-fill { fill: var(--viz-light); opacity: 0.08; }
.viz-svg .now { stroke: var(--text-muted); stroke-width: 1.5; stroke-dasharray: 6 5; }
.viz-svg .tachy-line { stroke: var(--violet); stroke-width: 2.5; stroke-dasharray: 8 6; }
.viz-svg .brady-line { stroke: var(--accent); stroke-width: 2.5; }
.viz-svg .frame-axis { stroke: var(--text-muted); stroke-width: 1.25; opacity: 0.7; }
.viz-svg .event { stroke: var(--surface-card); stroke-width: 3; }
.viz-svg .ev-a { fill: var(--text-strong); }
.viz-svg .ev-b { fill: var(--violet); }
.viz-svg .ev-c { fill: var(--accent); }
.viz-svg .hyper { fill: none; stroke: var(--border-default); stroke-width: 1; stroke-dasharray: 3 4; }
.viz-svg .curve { fill: none; stroke-width: 3; stroke-linecap: round; }
.viz-svg .curve-brady { stroke: var(--accent); }
.viz-svg .curve-tachy { stroke: var(--violet); }
.viz-svg .wall { stroke: var(--text-strong); stroke-width: 2; stroke-dasharray: 4 4; }
.viz-svg .wall-label { fill: var(--text-strong); font-weight: 600; font-size: 15px; }
.viz-svg .dot { stroke: var(--surface-card); stroke-width: 3; cursor: grab; }
.viz-svg .dot-brady { fill: var(--accent); }
.viz-svg .dot-tachy { fill: var(--violet); }
.viz-svg .dot:active { cursor: grabbing; }
.viz-svg .wave { fill: none; stroke: var(--viz-light); stroke-width: 1.25; opacity: 0.55; }
.viz-svg .shock { stroke: var(--cyan); stroke-width: 3; }
.viz-svg .shock-fill { fill: var(--cyan); opacity: 0.07; }
.viz-svg .particle { fill: var(--accent); stroke: var(--surface-card); stroke-width: 3; }
.viz-svg .medium { fill: var(--surface-sunken); }
.viz-svg .worldline { stroke: var(--text-strong); stroke-width: 2.5; }
.viz-svg .worldline-b { stroke: var(--accent); stroke-width: 2.5; }
.viz-svg .msg { stroke: var(--violet); stroke-width: 3; marker-end: url(#arrow-violet); }
.viz-svg .reply { stroke: var(--cyan-strong); stroke-width: 3; marker-end: url(#arrow-cyan); }
.viz-svg .bad { fill: var(--warn-text); }

:root {
  /* Text-safe tints of the brand colors for labels on cards (4.5:1 on --surface-card). */
  --violet-text: #6d28d9;
  --warn-text: #b42318;
  --viz-light: #d97706;
  --cyan-strong: #0891b2;
}

@media (prefers-color-scheme: dark) {
  :root {
    --violet-text: #b9a2ff;
    --warn-text: #ff8a80;
    --viz-light: #fbbf24;
    --cyan-strong: #22d3ee;
  }
}

.viz-controls {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
  gap: 12px 20px;
  margin-top: 16px;
}

.ctl {
  display: grid;
  grid-template-columns: 1fr auto;
  align-items: center;
  gap: 6px 12px;
}

.ctl-wide { grid-column: 1 / -1; }

.ctl-name {
  font-size: 14px;
  font-weight: 600;
  color: var(--text-strong);
}

.ctl-out {
  font-variant-numeric: tabular-nums;
  font-size: 14px;
  font-weight: 600;
  color: var(--pill-text);
}

.ctl input[type="range"] {
  grid-column: 1 / -1;
  width: 100%;
  accent-color: var(--accent);
  height: 28px;
  margin: 0;
}

.ctl input[type="range"]:focus-visible,
.check input:focus-visible,
.pill-radio input:focus-visible + span {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

.ctl-row {
  grid-column: 1 / -1;
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  align-items: center;
}

.check {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  font-size: 14px;
  color: var(--text-body);
}

.check input { accent-color: var(--accent); width: 18px; height: 18px; }

.pill-radio { position: relative; }
.pill-radio input { position: absolute; opacity: 0; inset: 0; margin: 0; cursor: pointer; }
.pill-radio span {
  display: inline-flex;
  align-items: center;
  height: 32px;
  padding: 0 14px;
  border-radius: 999px;
  border: 1px solid var(--border-default);
  font-size: 14px;
  font-weight: 600;
  color: var(--text-body);
}
.pill-radio input:checked + span {
  background: var(--accent-soft);
  border-color: transparent;
  color: var(--pill-text);
}

.phone-steps .btn[aria-pressed="true"] {
  border-color: var(--accent);
  color: var(--pill-text);
  background: var(--accent-soft);
}

.viz-readout {
  margin-top: 14px;
  padding: 12px 14px;
  border-radius: var(--radius-md);
  background: var(--accent-soft);
  color: var(--pill-text);
  font-size: 15px;
  font-weight: 500;
  line-height: 1.5;
}

.viz-readout .late { color: var(--pill-text); }
.viz-readout strong { color: inherit; }

.viz-note {
  margin: 12px 0 0 !important;
  font-size: 15px !important;
  color: var(--text-muted) !important;
}

/* 3D antitelephone */
.viz-stage-3d { aspect-ratio: 640 / 420; }
.phone-canvas {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  display: none;
  border-radius: var(--radius-md);
  cursor: grab;
  touch-action: none;
}
.phone-canvas:active { cursor: grabbing; }
.viz-3d.is-3d .phone-canvas { display: block; }
.viz-3d.is-3d .phone-fallback { visibility: hidden; }
.phone-badge {
  position: absolute;
  right: 10px;
  top: 10px;
  margin: 0 !important;
  padding: 4px 10px;
  border-radius: 999px;
  background: var(--surface-sunken);
  color: var(--text-muted) !important;
  font-size: 12px !important;
  pointer-events: none;
}
.phone-label {
  position: absolute;
  transform: translate(-50%, -50%);
  padding: 2px 8px;
  border-radius: 6px;
  background: var(--surface-card);
  border: 1px solid var(--border-subtle);
  font-size: 12px;
  font-weight: 600;
  color: var(--text-strong);
  white-space: nowrap;
  pointer-events: none;
}

/* Myths */
.myths { margin: 0; }
.myths dt {
  margin: 24px 0 6px;
  font-size: 18px;
  font-weight: 600;
  color: var(--text-strong);
}
.myths dd { margin: 0; }

/* Orbit cards */
.orbit-cards {
  list-style: none;
  margin: 16px 0 0;
  padding: 0;
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 12px;
}
.orbit-cards li {
  display: flex;
  flex-direction: column;
  padding: 16px;
  border-radius: var(--radius-lg);
  background: var(--surface-card);
  border: 1px solid var(--border-subtle);
  box-shadow: var(--shadow-sm);
}
.orbit-cards strong { display: block; margin-bottom: 6px; color: var(--text-strong); }
.orbit-cards span { display: block; flex: 1; font-size: 15px; line-height: 1.55; color: var(--text-body); }
.orbit-play { margin-top: 10px; font-size: 14px; font-weight: 600; }
.orbit-play::after { content: " \2192"; }

/* References */
.refs { padding-left: 22px; }
.refs li { font-size: 15px !important; margin-bottom: 8px; }
.refs li:target { background: var(--accent-soft); border-radius: 6px; }

@media (max-width: 980px) {
  .levels { top: 68px; }
  .levels-hint { display: none; }
}

@media (max-width: 620px) {
  .levels legend { position: absolute; width: 1px; height: 1px; overflow: hidden; clip: rect(0 0 0 0); }
  .levels-options { width: 100%; justify-content: space-between; }
  .levels-options label { flex: 1; }
  .levels-options span { justify-content: center; padding: 0 6px; font-size: 13px; }
  .viz { padding: 14px; margin-left: -8px; margin-right: -8px; }
  .explainer-body p, .explainer-body li, .explainer-body dd { font-size: 16px; }
}


/* The 3D view's labels (positioned by tachyon-3d.js). */
.phone-label.is-warn { color: var(--warn-text); }