.start-screen {
  position: fixed;
  inset: 0;
  z-index: 400;
  overflow-y: auto;
  color: var(--ink);
  background: var(--paper);
  transition: opacity 360ms ease, visibility 360ms ease;
}

.start-screen[hidden] { display: none !important; }
.start-screen.is-leaving { visibility: hidden; opacity: 0; }
body.start-screen-open { overflow: hidden; }

.start-shell {
  width: min(100%, 1440px);
  min-height: 100svh;
  margin: 0 auto;
  padding: 24px clamp(24px, 5vw, 80px) 30px;
}

.start-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 24px;
  min-height: 48px;
  padding-bottom: 12px;
  border-bottom: 3px double var(--rule-strong);
}

.start-brandline {
  display: flex;
  align-items: baseline;
  gap: 14px;
  font-family: var(--mono);
  letter-spacing: .09em;
  text-transform: uppercase;
}

.start-brandline strong { font-size: 13px; }
.start-brandline span { color: var(--muted); font-size: 11px; }

.start-main {
  display: grid;
  grid-template-columns: minmax(0, 1.35fr) minmax(320px, .65fr);
  min-height: calc(100svh - 132px);
  border-bottom: 1px solid var(--rule-strong);
}

.start-hero {
  display: flex;
  min-width: 0;
  flex-direction: column;
  justify-content: center;
  padding: clamp(52px, 8vh, 104px) clamp(30px, 5vw, 76px) clamp(50px, 8vh, 90px) 0;
}

.start-kicker,
.start-panel-kicker {
  margin: 0 0 14px;
  color: var(--head);
  font: 700 11px/1.4 var(--mono);
  letter-spacing: .13em;
  text-transform: uppercase;
}

.start-title {
  margin: 0;
  font-family: var(--serif);
  font-size: clamp(76px, 12vw, 174px);
  font-weight: 700;
  letter-spacing: -.07em;
  line-height: .78;
}

html[lang="zh-CN"] .start-title {
  letter-spacing: -.09em;
}

.start-welcome {
  max-width: 640px;
  margin: clamp(28px, 5vh, 54px) 0 0;
  color: var(--muted);
  font-family: var(--serif);
  font-size: clamp(18px, 2vw, 27px);
  line-height: 1.5;
  text-wrap: pretty;
}

.start-chain-sample {
  display: flex;
  align-items: baseline;
  flex-wrap: wrap;
  gap: 6px 10px;
  width: fit-content;
  max-width: 100%;
  margin-top: clamp(34px, 6vh, 70px);
  padding: 12px 0 11px;
  border-top: 1px solid var(--rule);
  border-bottom: 1px solid var(--rule);
  font-family: var(--mono);
  font-size: clamp(17px, 2.1vw, 28px);
}

.start-chain-sample .sample-word-start { color: var(--head); }
.start-chain-sample .sample-word-end { color: var(--overlap); }
.start-chain-sample .sample-arrow { color: var(--muted); }

.start-decision {
  display: flex;
  align-items: center;
  padding: clamp(40px, 7vh, 78px) 0 clamp(40px, 7vh, 78px) clamp(28px, 4vw, 64px);
  border-left: 1px solid var(--rule-strong);
}

.start-decision-inner { width: 100%; }

.start-decision h2 {
  max-width: 12ch;
  margin: 0;
  font-family: var(--serif);
  font-size: clamp(34px, 4.2vw, 61px);
  font-weight: 700;
  letter-spacing: -.035em;
  line-height: 1.02;
  text-wrap: balance;
}

html[lang="zh-CN"] .start-decision h2 { letter-spacing: -.02em; }

.start-decision-copy {
  max-width: 34ch;
  margin: 17px 0 28px;
  color: var(--muted);
  font-family: var(--serif);
  font-size: 15px;
  line-height: 1.6;
}

.start-actions { display: grid; gap: 9px; }

.start-action {
  min-height: 50px;
  padding: 12px 16px;
  border: 1px solid var(--rule-strong);
  color: var(--ink);
  background: transparent;
  font: 700 12px/1 var(--mono);
  letter-spacing: .08em;
  text-transform: uppercase;
  cursor: pointer;
  transition: color 180ms ease, background-color 180ms ease, transform 180ms ease, box-shadow 220ms ease;
}

.start-action:hover:not(:disabled) { background: rgb(255 255 255 / .35); }
.start-action:active:not(:disabled) { transform: translateY(1px); }

.start-action-primary {
  min-height: 58px;
  color: var(--paper);
  background: var(--ink);
  box-shadow: 5px 5px 0 var(--head);
}

.start-action-primary:hover:not(:disabled) {
  color: var(--paper);
  background: var(--head);
  box-shadow: 7px 7px 0 var(--ink);
  transform: translateY(-1px);
}

.start-action:disabled {
  color: var(--muted);
  background: var(--paper-deep);
  cursor: not-allowed;
  opacity: .66;
}

.start-login-note {
  margin-left: 7px;
  padding-left: 7px;
  border-left: 1px solid currentColor;
  font-size: 9px;
  font-weight: 400;
}

.start-mode-picker[hidden],
.start-welcome-panel[hidden],
.start-about[hidden] { display: none !important; }

.start-mode-list {
  display: grid;
  margin: 26px 0 12px;
  border-top: 1px solid var(--rule-strong);
}

.start-mode-option {
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto;
  align-items: center;
  gap: 18px;
  padding: 18px 0;
  border: 0;
  border-bottom: 1px solid var(--rule-strong);
  color: var(--ink);
  background: transparent;
  text-align: left;
  cursor: pointer;
}

.start-mode-option:hover .start-mode-name { color: var(--head); }
.start-mode-name { display: block; font-family: var(--serif); font-size: 28px; font-weight: 700; }
.start-mode-copy { display: block; margin-top: 4px; color: var(--muted); font-size: 12px; line-height: 1.45; }
.start-mode-arrow { color: var(--tail); font-family: var(--serif); font-size: 30px; transition: transform 180ms ease; }
.start-mode-option:hover .start-mode-arrow { transform: translateX(4px); }

.start-back {
  padding: 8px 0;
  border: 0;
  color: var(--muted);
  background: transparent;
  font: 11px/1.3 var(--mono);
  text-decoration: underline;
  text-underline-offset: 4px;
  cursor: pointer;
}

.start-footer {
  display: flex;
  justify-content: space-between;
  gap: 20px;
  padding-top: 12px;
  color: var(--muted);
  font: 10px/1.4 var(--mono);
  letter-spacing: .08em;
  text-transform: uppercase;
}

.start-about {
  position: fixed;
  inset: 0;
  z-index: 2;
  display: grid;
  place-items: center;
  padding: 22px;
  background: rgb(23 23 21 / .76);
}

.start-about-card {
  width: min(92vw, 620px);
  padding: clamp(24px, 5vw, 46px);
  border: 2px solid var(--ink);
  color: var(--ink);
  background: var(--paper);
  box-shadow: 10px 10px 0 rgb(0 0 0 / .22);
}

.start-about-head {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 24px;
  padding-bottom: 13px;
  border-bottom: 3px double var(--rule-strong);
}

.start-about-card h2 { margin: 0; font-family: var(--serif); font-size: 42px; }
.start-about-card p { margin: 18px 0 0; color: var(--muted); font-family: var(--serif); font-size: 17px; line-height: 1.7; }

.start-about-close {
  width: 38px;
  height: 38px;
  flex: 0 0 auto;
  border: 1px solid var(--rule-strong);
  color: var(--ink);
  background: transparent;
  font: 24px/1 var(--serif);
  cursor: pointer;
}

.start-about-close:hover { color: var(--paper); background: var(--ink); }

.start-home-link {
  padding: 4px 0;
  border: 0;
  border-bottom: 1px solid var(--rule-strong);
  color: var(--muted);
  background: transparent;
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: .06em;
  cursor: pointer;
}

.start-action:focus-visible,
.start-mode-option:focus-visible,
.start-back:focus-visible,
.start-about-close:focus-visible,
.start-home-link:focus-visible {
  outline: 2px solid var(--head);
  outline-offset: 3px;
}

.start-screen:not(.is-leaving) .start-kicker { animation: start-rise 480ms 60ms var(--motion-expo, ease-out) both; }
.start-screen:not(.is-leaving) .start-title { animation: start-rise 680ms 110ms var(--motion-expo, ease-out) both; }
.start-screen:not(.is-leaving) .start-welcome { animation: start-rise 560ms 210ms var(--motion-expo, ease-out) both; }
.start-screen:not(.is-leaving) .start-chain-sample { animation: start-rise 560ms 290ms var(--motion-expo, ease-out) both; }
.start-screen:not(.is-leaving) .start-decision-inner { animation: start-rise 620ms 240ms var(--motion-expo, ease-out) both; }

@keyframes start-rise {
  from { opacity: 0; transform: translateY(12px); }
  to { opacity: 1; transform: translateY(0); }
}

@media (max-width: 900px) {
  .start-main { grid-template-columns: minmax(0, 1fr); }
  .start-hero { min-height: 58svh; padding-right: 0; }
  .start-decision { padding: 42px 0; border-top: 1px solid var(--rule-strong); border-left: 0; }
  .start-decision h2 { max-width: 16ch; }
  .start-decision-copy { max-width: 48ch; }
}

@media (max-width: 560px) {
  .start-shell { padding: 14px 16px 22px; }
  .start-header { align-items: flex-start; }
  .start-brandline { display: grid; gap: 3px; }
  .start-title { font-size: clamp(68px, 25vw, 104px); line-height: .84; }
  .start-hero { min-height: 0; padding: 64px 0 54px; }
  .start-welcome { font-size: 18px; }
  .start-chain-sample { margin-top: 38px; font-size: 16px; }
  .start-decision { padding: 40px 0 50px; }
  .start-footer { flex-direction: column; gap: 5px; }
}

@media (prefers-reduced-motion: reduce) {
  .start-screen,
  .start-screen *,
  .start-mode-arrow { animation: none !important; transition: none !important; }
}