/*
 * The page borrows its vocabulary from an instrument approach plate: a cool paper ground,
 * condensed display type, tabular data set in mono, and a margin rail carrying the section
 * name the way a chart carries its segment annotations.
 */

:root {
  color-scheme: light dark;

  /* Ground and ink. The dark appearance is a lit instrument panel rather than pure black. */
  --plate: light-dark(#f5f7fa, #0d1117);
  --plate-raised: light-dark(#ffffff, #151b23);
  --plate-sunken: light-dark(#eaeff5, #11171e);
  --ink: light-dark(#0f1720, #e3eaf2);
  --ink-quiet: light-dark(#525f70, #99a7b8);
  --ink-faint: light-dark(#8593a3, #677484);
  --rule: light-dark(#d2dae4, #232c37);
  --rule-faint: light-dark(#e3e9f0, #1a212a);

  /* Both blues are the stops of the app icon's own gradient. */
  --beacon: light-dark(#2e4fa8, #8098f7);
  --beacon-strong: light-dark(#24408d, #9aadff);
  --beacon-wash: light-dark(#e8edfb, #19203a);
  --ice: light-dark(#badde6, #2a4550);

  /* Spent once, on the safety notice, and nowhere else. */
  --caution: light-dark(#8a5a00, #f0b429);
  --caution-wash: light-dark(#fdf3df, #241c08);
  --caution-rule: light-dark(#e6c98a, #5c4711);

  --display: "IBM Plex Sans Condensed", "Helvetica Neue", system-ui, sans-serif;
  --body: "IBM Plex Sans", system-ui, -apple-system, sans-serif;
  --data: "IBM Plex Mono", ui-monospace, "SF Mono", Menlo, monospace;

  --measure: 56ch;
  --wrap: 74rem;
  --rail-width: 8.5rem;
  --rail-gap: 3.5rem;
  --gap: 1.75rem;
  --section-gap: clamp(4rem, 9vw, 7rem);
  --radius: 0.25rem;
  --radius-panel: 0.625rem;
  --header-height: 4rem;
}

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

body {
  margin: 0;
  background: var(--plate);
  color: var(--ink);
  font: 400 1rem / 1.65 var(--body);
  font-variant-numeric: tabular-nums;
  text-wrap: pretty;
  -webkit-font-smoothing: antialiased;
}

h1,
h2,
h3 {
  margin: 0;
  font-family: var(--display);
  text-wrap: balance;
}

h1 {
  font-size: clamp(2.5rem, 5.4vw, 4.25rem);
  font-weight: 600;
  line-height: 0.95;
  letter-spacing: -0.02em;
}

h3 {
  font-size: 1.0625rem;
  font-weight: 600;
  line-height: 1.25;
  letter-spacing: -0.005em;
}

p {
  margin: 0 0 1em;
}

a {
  color: var(--beacon);
  text-underline-offset: 0.2em;
  text-decoration-thickness: 1px;
}

a:hover {
  color: var(--beacon-strong);
}

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

/* The element exists only to choose between the light and dark capture; the `img` it resolves to
   should lay out as though it were the parent's own child. Dropping `source` out of the box tree
   keeps it from being counted as a grid item alongside that `img`. */
picture {
  display: contents;
}

picture source {
  display: none;
}

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

[hidden] {
  display: none;
}

/* Layout primitives */

.wrap {
  width: min(100% - 2.5rem, var(--wrap));
  margin-inline: auto;
}

.prose {
  max-width: var(--measure);
}

.lede {
  max-width: 46ch;
  color: var(--ink-quiet);
  font-size: clamp(1.0625rem, 1.6vw, 1.25rem);
  line-height: 1.55;
}

.skip-link {
  position: absolute;
  inset-inline-start: -100vw;

  &:focus {
    position: static;
    display: inline-block;
    padding: 0.5rem 1rem;
    background: var(--plate-raised);
  }
}

/* The chart rail: section names live in the margin, as annotations rather than headlines. */

.rail {
  align-self: start;
  margin: 0 0 0.5rem;
  color: var(--ink-faint);
  font: 600 0.75rem / 1.4 var(--data);
  letter-spacing: 0.16em;
  text-transform: uppercase;
}

.section-grid {
  display: grid;
  grid-template-columns: minmax(0, 1fr);
  gap: 0 var(--rail-gap);
}

@media (width >= 60rem) {
  .section-grid {
    grid-template-columns: var(--rail-width) minmax(0, 1fr);
  }

  .rail {
    position: sticky;
    top: calc(var(--header-height) + 2rem);
    margin-bottom: 0;
    padding-top: 0.4rem;
  }
}

.section {
  padding-block: var(--section-gap);
  border-top: 1px solid var(--rule-faint);
}

.section-lede {
  max-width: 52ch;
  font-size: clamp(1.125rem, 1.7vw, 1.375rem);
  line-height: 1.5;
  letter-spacing: -0.01em;
}

/* Buttons */

.button {
  display: inline-flex;
  align-items: center;
  padding: 0.6rem 1.05rem;
  border: 1px solid transparent;
  border-radius: var(--radius);
  font: 600 0.9375rem / 1 var(--body);
  text-decoration: none;
  white-space: nowrap;
  transition: background-color 120ms ease, border-color 120ms ease, color 120ms ease;
}

.button-primary {
  background: var(--beacon);
  color: light-dark(#ffffff, #0d1117);

  &:hover {
    background: var(--beacon-strong);
    color: light-dark(#ffffff, #0d1117);
  }
}

.button-quiet {
  border-color: var(--rule);
  color: var(--ink);

  &:hover {
    border-color: var(--ink-quiet);
    color: var(--ink);
  }
}

.button-large {
  padding: 0.8rem 1.4rem;
  font-size: 1rem;
}

.cta-row {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
  margin-block: 1.75rem 1.25rem;
}

/* Header */

.site-header {
  position: sticky;
  top: 0;
  z-index: 20;
  background: color-mix(in srgb, var(--plate) 82%, transparent);
  backdrop-filter: saturate(180%) blur(14px);
  border-bottom: 1px solid var(--rule-faint);
}

.header-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--gap);
  min-height: var(--header-height);
}

.brand {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  color: var(--ink);
  font: 700 1.0625rem / 1 var(--display);
  letter-spacing: 0.005em;
  text-decoration: none;

  & img {
    border-radius: 23%;
  }
}

.nav-toggle {
  display: none;
  padding: 0.45rem 0.7rem;
  border: 1px solid var(--rule);
  border-radius: var(--radius);
  background: none;
  color: var(--ink-quiet);
  font: 600 0.6875rem / 1 var(--data);
  letter-spacing: 0.14em;
  text-transform: uppercase;
  cursor: pointer;
}

.site-nav {
  display: flex;
  align-items: center;
  gap: 1.75rem;

  & ul {
    display: flex;
    gap: 1.5rem;
    margin: 0;
    padding: 0;
    list-style: none;
  }

  & a:not(.button) {
    color: var(--ink-quiet);
    font-size: 0.9375rem;
    text-decoration: none;

    &:hover {
      color: var(--ink);
    }
  }
}

@media (width < 60rem) {
  .nav-toggle {
    display: block;
  }

  .site-nav {
    display: none;
    flex-direction: column;
    align-items: stretch;
    gap: 0.9rem;
    width: 100%;
    padding-block: 1.25rem 1.5rem;

    & ul {
      flex-direction: column;
      gap: 0.9rem;
    }

    & .button {
      justify-content: center;
    }
  }

  .header-inner:has(.nav-toggle[aria-expanded="true"]) {
    flex-wrap: wrap;

    & .site-nav {
      display: flex;
    }
  }
}

/* Hero */

.hero {
  padding-block: clamp(2.5rem, 5vw, 4rem) clamp(3rem, 6vw, 5rem);
  border-top: 0;
}

.hero-copy {
  display: grid;
  grid-template-columns: minmax(0, 1fr);
  gap: 0 4rem;
}

.hero-icon {
  border-radius: 23%;
  margin-bottom: 1.5rem;
}

.hero-copy h1 {
  max-width: 15ch;
}

/* The headline sets the measure; the lede and calls to action settle against its baseline. */
@media (width >= 60rem) {
  .hero-copy {
    grid-template-columns: minmax(0, 1.05fr) minmax(0, 0.95fr);
  }

  .hero-icon,
  .hero-copy h1 {
    grid-column: 1;
  }

  .hero-aside {
    grid-column: 2;
    grid-row: 2;
    align-self: end;
    padding-bottom: 0.5rem;
  }
}

.hero-aside .lede {
  max-width: 42ch;
  margin-top: 1.5rem;
}

.hero-meta {
  margin: 0;
  color: var(--ink-faint);
  font: 400 0.8125rem / 1.6 var(--data);
  letter-spacing: 0.02em;
}

/* Profile diagram — the signature element */

.diagram {
  margin: clamp(3rem, 6vw, 4.5rem) 0 0;
  padding: 1.25rem 1.25rem 1rem;
  background: var(--plate-raised);
  border: 1px solid var(--rule);
  border-radius: var(--radius-panel);
}

.diagram-head {
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  gap: 0.5rem 1.5rem;
  padding-bottom: 0.9rem;
  border-bottom: 1px solid var(--rule-faint);
  color: var(--ink-faint);
  font: 400 0.6875rem / 1.5 var(--data);
  letter-spacing: 0.13em;
  text-transform: uppercase;

  & b {
    color: var(--ink-quiet);
    font-weight: 600;
  }
}

.diagram-control {
  display: flex;
  align-items: center;
  gap: 0.75rem;

  & input[type="range"] {
    width: clamp(7rem, 13vw, 11rem);
    accent-color: var(--beacon);
    cursor: grab;
  }

  & input[type="range"]:active {
    cursor: grabbing;
  }

  /* Reserved so that dragging the slider never reflows the row around it. */
  & output {
    min-width: 17ch;
    color: var(--ink-quiet);
    font-weight: 600;
    text-align: end;
    white-space: nowrap;
  }
}

/* Too narrow for one row: the reading sits opposite its label, and the slider spans both. */
@media (width < 48rem) {
  .diagram-control {
    display: grid;
    grid-template-columns: auto minmax(0, 1fr);
    gap: 0.5rem 0.75rem;
    width: 100%;

    & label {
      grid-area: 1 / 1;
    }

    & output {
      grid-area: 1 / 2;
      min-width: 0;
    }

    & input[type="range"] {
      grid-area: 2 / 1 / 3 / -1;
      width: 100%;
    }
  }
}

.diagram-scroll {
  overflow-x: auto;
  overscroll-behavior-x: contain;
}

/* The floor keeps the labels legible; below it the chart pans, the way a chart does. */
.profile {
  display: block;
  width: 100%;
  min-width: 34rem;
  height: auto;
}

.profile .graticule {
  stroke: var(--rule-faint);
  stroke-width: 1;
}

.profile .graticule-label,
.profile .fix-label {
  fill: var(--ink-faint);
  font: 400 15px var(--data);
  letter-spacing: 0.1em;
}

.profile .dropline {
  stroke: var(--rule);
  stroke-width: 1;
  stroke-dasharray: 2 5;
}

.profile .ground {
  fill: var(--plate-sunken);
}

.profile .ground-line,
.profile .runway {
  stroke: var(--rule);
  stroke-width: 1;
}

.profile .runway {
  stroke: var(--ink-quiet);
  stroke-width: 5;
}

.profile .path-published {
  fill: none;
  stroke: var(--ink-quiet);
  stroke-width: 2.5;
  stroke-linejoin: round;
}

.profile .path-corrected {
  fill: none;
  stroke: var(--beacon);
  stroke-width: 3;
  stroke-linejoin: round;
}

.profile .alt-published {
  fill: var(--ink-quiet);
  font: 400 19px var(--data);
}

.profile .alt-corrected {
  fill: var(--beacon);
  font: 600 20px var(--data);
}

.profile .delta-brace {
  stroke: var(--beacon);
  stroke-width: 1.25;
}

.profile .delta-label {
  fill: var(--beacon);
  font: 600 16px var(--data);
  letter-spacing: 0.06em;
}

.diagram-legend {
  display: flex;
  flex-wrap: wrap;
  gap: 0.4rem 1.5rem;
  margin: 0.75rem 0 0;
  padding: 0;
  list-style: none;
  color: var(--ink-quiet);
  font: 400 0.75rem / 1.5 var(--data);
  letter-spacing: 0.08em;
  text-transform: uppercase;

  & li {
    display: flex;
    align-items: center;
    gap: 0.5rem;
  }

  & i {
    width: 1.5rem;
    height: 0;
    border-top: 3px solid var(--ink-quiet);
  }

  & .swatch-corrected {
    border-top-color: var(--beacon);
  }
}

.diagram-note {
  max-width: 68ch;
  margin: 1rem 0 0;
  color: var(--ink-faint);
  font-size: 0.8125rem;
  line-height: 1.5;
}

/* Safety notice — the only place the caution colour is spent. */

.notice {
  padding-block: 1.5rem;
  background: var(--caution-wash);
  border-block: 1px solid var(--caution-rule);
}

.notice .rail {
  color: var(--caution);
}

.notice-text {
  max-width: 68ch;
  margin: 0;
  font-size: 0.9375rem;

  & strong {
    color: var(--ink);
    font-weight: 600;
  }
}

/* How it works */

.how-grid {
  display: grid;
  grid-template-columns: minmax(0, 1fr);
  gap: 3rem;
  align-items: start;
}

@media (width >= 60rem) {
  .how-grid {
    grid-template-columns: minmax(0, 1.35fr) minmax(0, 1fr);
    gap: 4rem;
  }
}

.how-copy p {
  max-width: var(--measure);
  color: var(--ink-quiet);
}

.how-copy .section-lede {
  color: var(--ink);
}

/* The one place numbering is used, because picking, then choosing, then reading is a sequence.
   Each step also selects the screen it produces, so the list doubles as the screenshot picker. */

.steps {
  margin: 2.5rem 0 0;
  padding: 0;
  list-style: none;
  counter-reset: step;

  & li {
    border-top: 1px solid var(--rule-faint);
    counter-increment: step;
  }

  & button {
    position: relative;
    display: block;
    width: 100%;
    padding: 1.1rem 1rem 1.1rem 4rem;
    border: 0;
    background: none;
    color: inherit;
    font: inherit;
    text-align: start;
    cursor: pointer;
  }

  & button::before {
    content: counter(step, decimal-leading-zero);
    position: absolute;
    inset-inline-start: 1.5rem;
    top: 1.15rem;
    color: var(--beacon);
    font: 600 0.8125rem / 1.4 var(--data);
    letter-spacing: 0.08em;
  }

  /* Marks the step the panel is showing. Centred on the number beside it. */
  & button::after {
    content: "";
    position: absolute;
    inset-inline-start: 0.25rem;
    top: 1.37rem;
    border: 0.35rem solid transparent;
    border-inline-start-color: var(--beacon);
    opacity: 0;
    transition: opacity 180ms ease;
  }

  & [aria-selected="true"]::after {
    opacity: 1;
  }
}

.step-title {
  display: block;
  font-family: var(--display);
  font-size: 1.0625rem;
  font-weight: 600;
  line-height: 1.25;
  letter-spacing: -0.005em;
  transition: color 140ms ease;
}

.steps button:hover .step-title,
.steps [aria-selected="true"] .step-title {
  color: var(--beacon);
}

.step-note {
  display: block;
  max-width: 54ch;
  margin-top: 0.35rem;
  color: var(--ink-quiet);
  font-size: 0.9375rem;
}

/* The panels share one grid cell so the height never changes as they cross-fade. */
.how-shot {
  display: grid;
}

.how-shot [role="tabpanel"] {
  grid-area: 1 / 1;
  transition: opacity 260ms ease, visibility 0s;
}

.how-shot [role="tabpanel"][hidden] {
  display: block;
  opacity: 0;
  visibility: hidden;
  transition: opacity 260ms ease, visibility 0s 260ms;
}

.how-shot img {
  display: block;
  width: 100%;
  max-width: 17rem;
  margin-inline: auto;
  border: 1px solid var(--rule);
  border-radius: 1.75rem;
  box-shadow: 0 1.5rem 3rem light-dark(rgb(15 23 32 / 10%), rgb(0 0 0 / 45%));
}

/* Features — a specification list, not a deck of cards. */

.feature-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(min(100%, 18rem), 1fr));
  gap: 0 var(--gap);
  margin: 0;
  padding: 0;
  list-style: none;

  & li {
    padding: 1.15rem 0 1.5rem;
    border-top: 1px solid var(--rule);
  }

  & p {
    max-width: 44ch;
    margin: 0.4rem 0 0;
    color: var(--ink-quiet);
    font-size: 0.9375rem;
  }
}

/* Open source */

.open-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(min(100%, 16rem), 1fr));
  gap: var(--gap);
  margin: 0;
  padding: 0;
  list-style: none;

  & li {
    padding: 1.5rem;
    background: var(--plate-raised);
    border: 1px solid var(--rule);
    border-radius: var(--radius-panel);
  }

  & p {
    margin: 0.5rem 0 0;
    color: var(--ink-quiet);
    font-size: 0.9375rem;
  }
}

/* FAQ */

.faq {
  max-width: var(--measure);

  & details {
    border-top: 1px solid var(--rule-faint);
  }

  & details:last-of-type {
    border-bottom: 1px solid var(--rule-faint);
  }

  & summary {
    display: flex;
    align-items: baseline;
    justify-content: space-between;
    gap: 1.5rem;
    padding-block: 1.05rem;
    font-family: var(--display);
    font-size: 1.0625rem;
    font-weight: 600;
    list-style: none;
    cursor: pointer;
  }

  & summary::-webkit-details-marker {
    display: none;
  }

  & summary::after {
    content: "+";
    color: var(--beacon);
    font: 400 1.125rem / 1 var(--data);
  }

  & details[open] summary::after {
    content: "–";
  }

  & summary:hover {
    color: var(--beacon);
  }

  & p {
    margin: 0;
    padding-bottom: 1.25rem;
    color: var(--ink-quiet);
    font-size: 0.9375rem;
  }
}

/* Closing */

.closing {
  text-align: center;

  & h2 {
    font-size: clamp(2rem, 4vw, 3rem);
    font-weight: 600;
    line-height: 1;
    letter-spacing: -0.015em;
  }

  & .lede {
    margin-inline: auto;
  }

  & .cta-row {
    justify-content: center;
  }
}

/* Legal pages */

.legal {
  & h1 {
    font-size: clamp(2rem, 4vw, 2.75rem);
    margin-bottom: 1.5rem;
  }

  & h2 {
    margin-top: 2.75rem;
    margin-bottom: 0.65rem;
    font-size: 1.375rem;
    font-weight: 600;
    line-height: 1.2;
  }

  & h3 {
    margin-top: 2rem;
    margin-bottom: 0.5rem;
  }

  & p {
    color: var(--ink-quiet);
  }
}

.legal .legal-summary {
  padding: 1.25rem 1.5rem;
  background: var(--beacon-wash);
  border-radius: var(--radius-panel);
  color: var(--ink);
  font-size: 1.0625rem;
}

/* Footer */

.site-footer {
  padding-block: 3.5rem;
  background: var(--plate-sunken);
  border-top: 1px solid var(--rule-faint);
  color: var(--ink-faint);
  font-size: 0.875rem;
}

.footer-inner {
  display: grid;
  gap: 1.25rem;
  justify-items: start;
}

.footer-brand {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  margin: 0;
  color: var(--ink);
  font: 700 1rem / 1 var(--display);

  & img {
    border-radius: 23%;
  }
}

.site-footer nav ul {
  display: flex;
  flex-wrap: wrap;
  gap: 1.5rem;
  margin: 0;
  padding: 0;
  list-style: none;
}

.site-footer a {
  color: var(--ink-quiet);
  text-decoration: none;

  &:hover {
    color: var(--ink);
  }
}

.footer-fine {
  max-width: 60ch;
  margin: 0;
  line-height: 1.6;
}

/* Motion: one orchestrated page-load sequence, and nothing else. */

@keyframes rise {
  from {
    opacity: 0;
    transform: translateY(0.75rem);
  }
}

@keyframes trace {
  from {
    stroke-dashoffset: 1600;
  }
}

@keyframes reveal {
  from {
    opacity: 0;
  }
}

.hero-icon,
.hero-copy h1,
.hero-aside > * {
  animation: rise 600ms cubic-bezier(0.2, 0.7, 0.3, 1) backwards;
}

.hero-copy h1 {
  animation-delay: 80ms;
}

.hero-aside > :nth-child(1) {
  animation-delay: 160ms;
}

.hero-aside > :nth-child(2) {
  animation-delay: 220ms;
}

.hero-aside > :nth-child(3) {
  animation-delay: 280ms;
}

.profile .path-published,
.profile .path-corrected {
  stroke-dasharray: 1600;
  animation: trace 1100ms cubic-bezier(0.3, 0.8, 0.4, 1) 300ms backwards;
}

.profile .path-corrected {
  animation-delay: 600ms;
}

.profile .annotation {
  animation: reveal 500ms ease-out 1400ms backwards;
}

@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation-duration: 1ms !important;
    animation-delay: 0ms !important;
    transition-duration: 1ms !important;
    transition-delay: 0ms !important;
  }
}