/*
 * The landing page: a hero, feature cards, and sections that arrive as you scroll.
 *
 * Three rules this file keeps, each of which is the difference between a nice page and a page that
 * fails somebody:
 *
 * 1. EVERY COLOUR IS A MATERIAL VARIABLE. The site has a light and a dark palette with a toggle.
 *    A literal background is the one thing guaranteed to look wrong in one of the two.
 *
 * 2. CONTENT IS VISIBLE BY DEFAULT. The reveal animation is opt-in: landing.js adds
 *    `data-reveal="on"` to the page, and only then does anything start hidden. With JavaScript
 *    off, broken or still loading, every section is simply there. A documentation front page that
 *    needs JavaScript to show its text is not a documentation front page.
 *
 * 3. prefers-reduced-motion TURNS IT OFF. Motion that cannot be refused is an accessibility
 *    problem, not a flourish, and this is a page somebody may be reading because they are stuck.
 */

/* ---------------------------------------------------------------- the hero */

.ob-hero {
  margin: 0 0 3rem;
  padding: 2.5rem 0 2rem;
  text-align: center;
  border-bottom: 1px solid var(--md-default-fg-color--lightest);
}

.ob-hero h1 {
  margin: 0 0 0.6rem;
  font-size: 2.4rem;
  font-weight: 700;
  line-height: 1.15;
  letter-spacing: -0.02em;
}

.ob-hero .ob-tagline {
  max-width: 34rem;
  margin: 0 auto 1.4rem;
  font-size: 1rem;
  line-height: 1.6;
  color: var(--md-default-fg-color--light);
}

.ob-hero .ob-buttons {
  display: flex;
  flex-wrap: wrap;
  gap: 0.6rem;
  justify-content: center;
}

.ob-hero .ob-sub {
  margin-top: 1rem;
  font-size: 0.7rem;
  color: var(--md-default-fg-color--light);
}

/* ------------------------------------------------------------ feature grid */

.ob-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(14rem, 1fr));
  gap: 1rem;
  margin: 1.5rem 0 2.5rem;
}

.ob-card {
  padding: 1.1rem 1.2rem;
  background: var(--md-code-bg-color);
  border: 1px solid var(--md-default-fg-color--lightest);
  border-radius: 0.3rem;
}

.ob-card h3 {
  margin: 0 0 0.4rem;
  font-size: 0.86rem;
  font-weight: 700;
}

.ob-card p {
  margin: 0;
  font-size: 0.78rem;
  line-height: 1.55;
  color: var(--md-default-fg-color--light);
}

.ob-card .ob-icon {
  display: block;
  margin-bottom: 0.5rem;
  color: var(--md-primary-fg-color);
}

.ob-card .ob-icon svg {
  width: 1.4rem;
  height: 1.4rem;
  fill: currentcolor;
}

/* A number worth staring at: 159 patterns, 1744 tests, two Protege versions. */
.ob-figures {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(8rem, 1fr));
  gap: 0.8rem;
  margin: 1.5rem 0 2.5rem;
  text-align: center;
}

.ob-figure strong {
  display: block;
  font-size: 1.7rem;
  font-weight: 700;
  line-height: 1.1;
  color: var(--md-primary-fg-color);
}

.ob-figure span {
  font-size: 0.7rem;
  line-height: 1.4;
  color: var(--md-default-fg-color--light);
}

/* ------------------------------------------------- before and after, as prose */

.ob-compare {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(16rem, 1fr));
  gap: 1rem;
  margin: 1.5rem 0 2.5rem;
}

.ob-compare > div {
  padding: 1rem 1.1rem;
  border-radius: 0.3rem;
}

.ob-without {
  background: var(--md-code-bg-color);
  border-left: 3px solid var(--md-default-fg-color--lighter);
}

.ob-with {
  background: var(--md-code-bg-color);
  border-left: 3px solid var(--md-primary-fg-color);
}

.ob-compare h3 {
  margin: 0 0 0.5rem;
  font-size: 0.8rem;
  text-transform: uppercase;
  letter-spacing: 0.05em;
}

.ob-compare ul {
  margin: 0;
  padding-left: 1.1rem;
  font-size: 0.78rem;
  line-height: 1.6;
  color: var(--md-default-fg-color--light);
}

/* ------------------------------------------------------- reveal on scroll */

/*
 * Opt-in, and only once the script has said so. Without [data-reveal="on"] on the page these
 * rules do not apply at all, so no-JS readers see the finished page rather than an empty one.
 */
[data-reveal="on"] .ob-reveal {
  opacity: 0;
  transform: translateY(1rem);
  transition: opacity 0.5s ease-out, transform 0.5s ease-out;
  will-change: opacity, transform;
}

[data-reveal="on"] .ob-reveal.ob-shown {
  opacity: 1;
  transform: none;
}

/* Staggered, so a grid arrives as a grid rather than as one block. */
[data-reveal="on"] .ob-reveal.ob-shown .ob-card:nth-child(2),
[data-reveal="on"] .ob-reveal.ob-shown .ob-figure:nth-child(2) {
  transition-delay: 0.06s;
}

[data-reveal="on"] .ob-reveal.ob-shown .ob-card:nth-child(3),
[data-reveal="on"] .ob-reveal.ob-shown .ob-figure:nth-child(3) {
  transition-delay: 0.12s;
}

[data-reveal="on"] .ob-reveal.ob-shown .ob-card:nth-child(4),
[data-reveal="on"] .ob-reveal.ob-shown .ob-figure:nth-child(4) {
  transition-delay: 0.18s;
}

/*
 * Somebody who has asked their system for less motion gets none, including no transition. Written
 * as `revert` rather than as a second set of values so there is one definition of "normal".
 */
@media (prefers-reduced-motion: reduce) {
  [data-reveal="on"] .ob-reveal,
  [data-reveal="on"] .ob-reveal.ob-shown {
    opacity: 1;
    transform: none;
    transition: none;
    will-change: auto;
  }
}

/* ------------------------------------------------------------------ mobile */

@media screen and (max-width: 44.9375em) {
  .ob-hero {
    padding: 1.5rem 0 1.2rem;
  }

  .ob-hero h1 {
    font-size: 1.8rem;
  }

  .ob-figure strong {
    font-size: 1.4rem;
  }
}