:root {
  --paper: #f7f4ec; --ink: #20312d; --muted: #5d6b66; --sage: #799782;
  --sage-dark: #365e4b; --blue: #7189a6; --line: #cbd5ce; --white: #fffdfa;
}
* { box-sizing: border-box; }
.train-bridge-page { margin: 0; background: linear-gradient(180deg,#f4f0e6,#fbfaf6); color: var(--ink); font-family: Inter,"PingFang SC","Microsoft YaHei",sans-serif; }
.train-main { width: min(1420px,calc(100% - 32px)); margin: auto; padding: 36px 0 110px; }
.tool-heading { max-width: 930px; margin-bottom: 24px; }
.tool-heading h1 { font-size: clamp(30px,4vw,52px); line-height: 1.12; margin: 8px 0; color: var(--ink); }
.eyebrow { color: var(--sage-dark); font-weight: 800; letter-spacing: .08em; }
.lead { font-size: 18px; color: var(--muted); }
.chips { display: flex; gap: 8px; flex-wrap: wrap; }
.chip { padding: 7px 12px; border-radius: 999px; background: #e5ede6; color: #294c3b; }
.bridge-lab { display: grid; grid-template-columns: minmax(0,1.75fr) minmax(300px,.72fr); gap: 18px; align-items: stretch; background: transparent; color: var(--ink); }
.stage-panel,.controls { background: rgba(255,253,250,.98); border: 1px solid #cfd9d1; border-radius: 24px; box-shadow: 0 18px 50px rgba(50,68,59,.09); color: var(--ink); }
.stage-panel { padding: 20px; }
.stage-head { display: flex; justify-content: space-between; gap: 16px; align-items: flex-start; padding: 12px; border-radius: 16px; background: #edf3ee; color: var(--ink); }
.stage-head p { margin: 0; color: #365e4b; font-weight: 800; }
.stage-head h2 { margin: 5px 0 0; font-size: 24px; color: var(--ink); }
.train-bridge-page .stage-actions button { min-width: 44px; min-height: 44px; color: #294c3b; background: #fffdfa; border: 1px solid #9caf9f; }
.known-strip { display: flex; gap: 10px; margin: 16px 0; }
.known-strip span { background: #e7eee8; color: #263d35; border-radius: 12px; padding: 10px 14px; }
.rail-board { position: relative; min-height: 430px; overflow: hidden; border-radius: 20px; background: linear-gradient(#dce8e7 0 55%,#e4d9c4 55%); border: 1px solid #b6c9c0; }
.rail-board [hidden], .phase-actions [hidden] { display: none !important; }
.bridge-deck { position: absolute; top: 52%; height: 74px; background: #8799a9; border: 8px solid #536979; border-radius: 8px; display: flex; justify-content: space-around; }
.bridge-deck span { width: 5px; background: #d7e0e5; transform: skew(-25deg); }
.boundary { position: absolute; top: 20%; bottom: 17%; z-index: 2; }
.boundary i { display: block; height: 100%; border-left: 3px dashed #31574a; }
.boundary span { background: #fffdfa; color: #20312d; padding: 5px 8px; border-radius: 8px; font-weight: 800; }
.journey-track { position: absolute; top: 12%; height: 38px; border: 2px solid #6e8277; border-radius: 10px; overflow: visible; background: #f8faf7; display: flex; }
.journey-track i { display: block; height: 100%; width: 0; opacity: 0; transition: opacity 160ms ease; }
.journey-track .bridge-segment.placed { background: #90a8be; opacity: 1; }
.journey-track .train-segment.placed { background: #91aa92; opacity: 1; }
.journey-track span { position: absolute; z-index: 2; max-width: calc(100% - 8px); padding: 0 4px; border-radius: 4px; color: #152d28; background: rgba(255,253,250,.9); font-size: 11px; line-height: 16px; font-weight: 800; white-space: nowrap; transform: translateX(-50%); }
.journey-track .bridge-caption { top: 1px; border-bottom: 2px solid #597590; }
.journey-track .train-caption { top: 18px; border-bottom: 2px solid #52785a; }
.train-hit { position: absolute; top: 58%; height: 72px; min-width: 44px; min-height: 72px; padding: 0; border: 0; background: transparent; z-index: 4; cursor: grab; touch-action: none; }
.train-bridge-page .train-hit:active { transform: none !important; }
.train-hit:focus-visible { outline: 4px solid #d8782f; outline-offset: 3px; }
.train-visual { position: absolute; top: 0; height: 72px; display: flex; flex-direction: row-reverse; filter: drop-shadow(0 8px 7px rgba(30,45,40,.22)); pointer-events: none; }
.train-visual > span { min-width: 0; display: flex; align-items: center; justify-content: center; border: 3px solid #365d50; background: #799782; color: #fff; overflow: hidden; }
.train-visual .engine { width: 42%; border-radius: 9px 18px 5px 5px; }
.train-visual .carriage { width: 38%; background: #91a8bd; }
.train-visual .tail { width: 20%; border-radius: 5px; }
.train-visual b { font-size: 11px; white-space: nowrap; }
.train-visual.compact b { display: none; }
.measure-rail { position: absolute; left: 6%; right: 6%; bottom: 5%; min-height: 54px; display: flex; gap: 10px; align-items: center; padding: 7px; border: 2px dashed #9aaea2; border-radius: 12px; background: #f8f5ec; }
.measure-slot { min-height: 38px; flex: 1; display: flex; align-items: center; justify-content: center; color: #2f4940; font-size: 13px; font-weight: 800; border-radius: 8px; background: #e5ece7; }
.measure-slot.used { opacity: .35; text-decoration: line-through; }
.board-note,.live-status { margin: 12px 0 0; color: var(--muted); }
.proof { background: #e7efe7; color: #20312d; border-left: 5px solid var(--sage); padding: 12px 16px; border-radius: 12px; }
.proof h3,.proof ol { margin: 4px 0; }.proof ol { padding-left: 22px; }
.controls { padding: 20px; display: flex; flex-direction: column; gap: 13px; }
.control-title span { font-size: 12px; letter-spacing: .12em; color: var(--sage-dark); font-weight: 800; }
.control-title h2 { margin: 4px 0; color: var(--ink); }
fieldset { border: 0; padding: 0; margin: 0; } legend { font-weight: 800; margin-bottom: 8px; color: var(--ink); }
.preset-grid,.phase-actions { display: grid; grid-template-columns: 1fr 1fr; gap: 8px; }
.controls button,.controls input { min-height: 44px; border: 1px solid #aabcb1; border-radius: 11px; background: #fff; color: #243a32; padding: 9px 12px; font: inherit; }
.controls button { cursor: pointer; font-weight: 750; }.controls button:disabled { opacity: .58; cursor: not-allowed; color: #53635d; }
.primary-action,#checkAction { background: var(--sage-dark) !important; color: #fff !important; border-color: var(--sage-dark) !important; }
.parameter-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 10px; }
.parameter-grid label,.answer-field { display: grid; gap: 6px; font-size: 14px; font-weight: 750; color: #273d35; }
.answer-field input[aria-invalid="true"] { border: 2px solid #a34737; background: #fff4f0; }
.secondary-actions { display: flex; gap: 8px; }.secondary-actions button { flex: 1; }
.operation-hint,.grade-boundary { margin: 0; color: #566660; font-size: 13px; }.grade-boundary { border-top: 1px solid var(--line); padding-top: 12px; }
.dragging { cursor: grabbing; }.settled .rail-board { box-shadow: inset 0 0 0 4px #76977c; }
body.classroom-screen.train-bridge-page .bridge-lab,
body.classroom-screen.train-bridge-page .stage-panel,
body.classroom-screen.train-bridge-page .controls,
#bridgeLab:fullscreen { background: #f7f4ec !important; color: #20312d !important; }
body.classroom-screen.train-bridge-page .stage-head,
#bridgeLab:fullscreen .stage-head { background: #dfe9e1 !important; color: #20312d !important; }
body.classroom-screen.train-bridge-page .stage-head h2,
body.classroom-screen.train-bridge-page .stage-head p,
body.classroom-screen.train-bridge-page .controls,
body.classroom-screen.train-bridge-page .controls h2,
body.classroom-screen.train-bridge-page .controls label,
body.classroom-screen.train-bridge-page .operation-hint,
body.classroom-screen.train-bridge-page .grade-boundary,
#bridgeLab:fullscreen .stage-head h2,
#bridgeLab:fullscreen .stage-head p,
#bridgeLab:fullscreen .controls,
#bridgeLab:fullscreen .controls h2,
#bridgeLab:fullscreen .controls label,
#bridgeLab:fullscreen .operation-hint,
#bridgeLab:fullscreen .grade-boundary { color: #20312d !important; }
body.classroom-screen.train-bridge-page .stage-actions button,
#bridgeLab:fullscreen .stage-actions button { color: #244437 !important; background: #fffdfa !important; border-color: #718b7c !important; }
body.classroom-screen.train-bridge-page #boardNote,
body.classroom-screen.train-bridge-page #liveStatus,
#bridgeLab:fullscreen #boardNote,
#bridgeLab:fullscreen #liveStatus { color: #3f514a !important; }
.train-bridge-page .classroom-screen-toggle { flex: 0 0 auto; min-width: 118px; min-height: 44px; overflow: visible; }
.train-bridge-page .fullscreen-button { flex: 0 0 44px; width: 44px; height: 44px; min-height: 44px; }
@media(max-width:820px) { .bridge-lab { grid-template-columns: minmax(0,1.65fr) minmax(260px,.9fr); }.train-main { width: min(100% - 20px,800px); }.stage-panel,.controls { padding: 14px; }.rail-board { min-height: 390px; }.site-links { display: none; } }
@media(max-width:620px) { .bridge-lab { grid-template-columns: 1fr; }.controls { order: 2; }.stage-panel { order: 1; }.rail-board { min-height: 360px; }.train-main { padding-top: 22px; }.stage-head { display: block; } }
@media(prefers-reduced-motion:reduce) { *,*::before,*::after { scroll-behavior: auto !important; transition: none !important; animation: none !important; } }