/* Opening sequence. CSS owns the whole timeline; prelude.js only reacts to the exit. */
.prelude {
  --impact: 2.8s;
  --exit: 3.65s;
  position: fixed;
  inset: 0;
  z-index: 100;
  display: none;
  grid-template-rows: 1fr auto;
  overflow: hidden;
  background: var(--paper);
}

.js .prelude {
  display: grid;
  animation: prelude-exit 1.1s cubic-bezier(.22, .7, .2, 1) var(--exit) forwards;
}

/* A second keyframe name restarts the exit from zero instead of jumping into it. */
.js .prelude.is-skipped {
  animation-name: prelude-exit-now;
  animation-delay: 0s;
}

.prelude.is-leaving {
  pointer-events: none;
}

.prelude::before {
  content: "";
  position: absolute;
  top: 46%;
  left: 50%;
  width: 10vmin;
  height: 10vmin;
  border: 1px solid rgb(228 60 74 / .62);
  border-radius: 50%;
  opacity: 0;
  transform: translate(-50%, -50%) scale(.4);
  pointer-events: none;
  animation: heart-ring 1.8s cubic-bezier(.08, .68, .16, 1) var(--impact);
}

.prelude::after {
  content: "";
  position: absolute;
  inset: 0;
  background: radial-gradient(circle at 50% 46%, rgb(228 60 74 / .12), rgb(228 60 74 / .035) 22%, transparent 48%);
  opacity: 0;
  pointer-events: none;
  animation: paper-flash 1.55s ease-out var(--impact);
}

.prelude__core {
  position: absolute;
  top: 50%;
  left: 50%;
  width: min(38vw, 450px);
  aspect-ratio: 1;
  border-radius: 50%;
  background: radial-gradient(circle, rgb(228 60 74 / .14), rgb(228 60 74 / .025) 46%, transparent 72%);
  opacity: 0;
  transform: translate(-50%, -50%) scale(.82);
  animation: core-bloom 1.9s ease-out var(--impact);
}

.prelude__stage {
  position: relative;
  display: grid;
  place-items: center;
  padding: 6vw;
}

.prelude__title {
  position: relative;
  z-index: 2;
  text-align: center;
  animation: title-arrive .8s cubic-bezier(.2, .8, .2, 1) both;
}

.prelude__kicker {
  color: var(--red);
  font: 11px var(--font-mono);
  letter-spacing: .42em;
}

.prelude__name {
  display: block;
  margin: 35px 0;
  font-size: clamp(4rem, 14vw, 11rem);
  line-height: .8;
  letter-spacing: -.07em;
  animation: title-breathe .9s cubic-bezier(.18, .82, .22, 1) var(--impact);
}

.prelude__trace {
  position: relative;
  display: flex;
  align-items: center;
  height: 116px;
  overflow: hidden;
  border-top: 1px solid var(--ink);
}

.prelude__trace::after {
  content: "";
  position: absolute;
  inset: 0;
  background: linear-gradient(90deg, transparent 0 97%, var(--paper) 100%);
  pointer-events: none;
}

.prelude__trace svg {
  width: 100%;
  height: 100%;
  overflow: visible;
}

.prelude__signal {
  position: absolute;
  right: 3vw;
  bottom: 12px;
  z-index: 2;
  color: var(--red);
  font: 10px var(--font-mono);
  letter-spacing: .2em;
}

.trace {
  fill: none;
  stroke-linecap: round;
  stroke-linejoin: round;
  stroke-dasharray: 1;
  stroke-dashoffset: 1;
}

.trace--track {
  stroke: var(--ink);
  stroke-width: 1;
  stroke-dasharray: none;
  stroke-dashoffset: 0;
  opacity: .1;
}

.trace--calm {
  stroke: var(--blue);
  stroke-width: 2;
  opacity: .72;
  animation: calm-cycle 1.55s cubic-bezier(.3, .05, .25, 1) .15s forwards;
}

.trace--beat {
  stroke: var(--red);
  stroke-width: 2.7;
  animation:
    pulse-write 1.55s linear 1.82s forwards,
    beat-glow .35s ease var(--impact) forwards;
}

@keyframes prelude-exit {
  to { opacity: 0; filter: blur(3px); transform: scale(1.012); visibility: hidden; }
}

@keyframes prelude-exit-now {
  to { opacity: 0; filter: blur(3px); transform: scale(1.012); visibility: hidden; }
}

@keyframes calm-cycle {
  0% { stroke-dashoffset: 1; opacity: .72; }
  55% { stroke-dashoffset: 0; opacity: .72; }
  68% { stroke-dashoffset: 0; opacity: .72; }
  92% { opacity: .35; }
  100% { stroke-dashoffset: -1; opacity: 0; }
}

@keyframes pulse-write {
  0% { stroke-dashoffset: 1; }
  35% { stroke-dashoffset: .72; }
  54% { stroke-dashoffset: .54; }
  63% { stroke-dashoffset: .29; }
  78% { stroke-dashoffset: .15; }
  100% { stroke-dashoffset: 0; }
}

@keyframes beat-glow {
  to { filter: drop-shadow(0 0 8px rgb(228 60 74 / .72)); }
}

@keyframes title-arrive {
  from { opacity: 0; transform: translateY(8px); }
}

@keyframes title-breathe {
  0%, 100% { transform: scale(1); }
  22% { transform: scale(1.016); }
  48% { transform: scale(.998); }
  72% { transform: scale(1.004); }
}

@keyframes heart-ring {
  0% { opacity: .42; transform: translate(-50%, -50%) scale(.4); }
  55% { opacity: .17; }
  100% { opacity: 0; transform: translate(-50%, -50%) scale(8); }
}

@keyframes paper-flash {
  0% { opacity: 0; }
  20% { opacity: 1; }
  62% { opacity: .36; }
  100% { opacity: 0; }
}

@keyframes core-bloom {
  0% { opacity: 0; transform: translate(-50%, -50%) scale(.82); }
  22% { opacity: .78; transform: translate(-50%, -50%) scale(1.02); }
  58% { opacity: .26; transform: translate(-50%, -50%) scale(1.1); }
  100% { opacity: 0; transform: translate(-50%, -50%) scale(1.2); }
}