:root {
            --bg-color: #0c1c30;
            --container-bg: #112743;
            --panel-bg: #17304f;
            --border-color: #2a4a72;
            --grid-line: rgba(93, 154, 219, 0.12);
            --panel-sunken: rgba(0, 0, 0, 0.3);
            --text-primary: #e8eff8;
            --text-secondary: #93aecb;
            --accent-blue: #4da3ff;
            --accent-amber: #e0a458;
            --accent-red: #f0596a;
            --accent-green: #4ade80;
            --display-font: 'Oswald', sans-serif;
            --mono-font: 'IBM Plex Mono', monospace;
            --shadow-color: rgba(0, 0, 0, 0.55);

            /* Shared kit mapping */
            --kit-accent: var(--accent-blue);
            --kit-accent-ink: #04182f;
            --kit-accent-glow: rgba(77, 163, 255, 0.25);
            --kit-surface: var(--panel-bg);
            --kit-border: var(--border-color);
            --kit-input-bg: var(--container-bg);
            --kit-error: var(--accent-red);
        }

        body.light-mode {
            --bg-color: #f6f7fa;
            --container-bg: #ffffff;
            --panel-bg: #eef2f8;
            --border-color: #c7d2e2;
            --grid-line: rgba(29, 78, 216, 0.08);
            --panel-sunken: rgba(0, 0, 0, 0.045);
            --text-primary: #10233f;
            --text-secondary: #4c6584;
            --accent-blue: #1d4ed8;
            --accent-amber: #b45309;
            --accent-red: #b91c1c;
            --accent-green: #15803d;
            --shadow-color: rgba(16, 35, 63, 0.12);

            /* Shared kit mapping (light theme) */
            --kit-accent: var(--accent-blue);
            --kit-accent-ink: #f5f8ff;
            --kit-accent-glow: rgba(29, 78, 216, 0.15);
            --kit-surface: var(--panel-bg);
            --kit-border: var(--border-color);
            --kit-input-bg: var(--container-bg);
            --kit-error: var(--accent-red);
        }

        * {
            box-sizing: border-box;
            margin: 0;
            padding: 0;
            transition: background-color 0.25s ease, color 0.25s ease, border-color 0.25s ease;
        }

        body {
            background-color: var(--bg-color);
            background-image:
                linear-gradient(var(--grid-line) 1px, transparent 1px),
                linear-gradient(90deg, var(--grid-line) 1px, transparent 1px);
            background-size: 24px 24px;
            color: var(--text-primary);
            font-family: var(--mono-font);
            min-height: 100vh;
            display: flex;
            flex-direction: column;
            align-items: center;
            justify-content: center;
            padding: 20px;
        }

        .top-controls {
            position: fixed;
            top: 20px;
            right: 24px;
            z-index: 1000;
        }

        .theme-toggle-btn {
            background: var(--container-bg);
            color: var(--text-primary);
            border: 2px solid var(--border-color);
            padding: 8px 16px;
            border-radius: 4px;
            font-family: var(--mono-font);
            font-weight: 600;
            font-size: 0.85rem;
            cursor: pointer;
            box-shadow: 0 4px 10px var(--shadow-color);
        }

        .theme-toggle-btn:hover {
            border-color: var(--accent-blue);
        }

        .blueprint-container {
            width: 100%;
            max-width: 860px;
            background: var(--container-bg);
            border: 2px solid var(--border-color);
            border-top: 6px solid var(--accent-blue);
            border-radius: 6px;
            padding: 32px;
            box-shadow: 0 12px 30px var(--shadow-color);
            min-height: 580px;
            display: flex;
            flex-direction: column;
            justify-content: space-between;
        }

        .hero-icon {
            font-size: 3rem;
            margin-bottom: 8px;
        }

        .blueprint-title {
            font-family: var(--display-font);
            font-size: 1.8rem;
            font-weight: 700;
            color: var(--accent-blue);
            text-align: center;
            letter-spacing: 0.5px;
            margin-bottom: 8px;
            text-transform: uppercase;
        }

        .blueprint-subtitle {
            font-family: var(--mono-font);
            text-align: center;
            color: var(--text-secondary);
            font-size: 0.9rem;
            margin-bottom: 20px;
            letter-spacing: 0.5px;
        }

        .screen-center {
            display: flex;
            flex-direction: column;
            align-items: center;
            justify-content: center;
            text-align: center;
            padding: 10px 0;
        }

        .brief-box {
            background: var(--panel-bg);
            border: 1px solid var(--border-color);
            border-radius: 4px;
            padding: 20px 28px;
            text-align: left;
            margin: 16px 0;
            max-width: 680px;
            line-height: 1.7;
            font-size: 0.92rem;
        }

        .brief-box ul { padding-left: 20px; }
        .brief-box li { margin-bottom: 8px; }

        .action-btn {
            background: var(--accent-blue);
            color: #ffffff;
            border: none;
            padding: 14px 36px;
            font-family: var(--display-font);
            font-size: 1rem;
            font-weight: 600;
            text-transform: uppercase;
            letter-spacing: 1px;
            cursor: pointer;
            margin-top: 18px;
            border-radius: 4px;
            box-shadow: 0 4px 12px var(--shadow-color);
        }

        .action-btn:hover { opacity: 0.92; }

        /* HUD Bar */
        .hud-bar {
            display: flex;
            justify-content: space-between;
            align-items: center;
            background: var(--panel-bg);
            border: 1px solid var(--border-color);
            padding: 12px 20px;
            margin-bottom: 18px;
            border-radius: 4px;
            gap: 12px;
            flex-wrap: wrap;
        }

        .hud-item {
            display: flex;
            flex-direction: column;
            font-size: 0.9rem;
        }

        .hud-label {
            font-size: 0.7rem;
            color: var(--text-secondary);
            text-transform: uppercase;
            letter-spacing: 0.5px;
        }

        .hud-value {
            font-weight: 700;
            color: var(--accent-blue);
        }

        /* Question Box */
        .span-card {
            background: var(--panel-bg);
            border: 1px solid var(--border-color);
            border-left: 4px solid var(--accent-blue);
            border-radius: 4px;
            padding: 20px 24px;
            margin-bottom: 18px;
        }

        .span-tag {
            font-family: var(--mono-font);
            font-size: 0.72rem;
            text-transform: uppercase;
            color: var(--accent-blue);
            font-weight: 700;
            margin-bottom: 8px;
            letter-spacing: 1px;
        }

        .span-text {
            font-family: var(--display-font);
            font-size: 1.15rem;
            line-height: 1.6;
            font-weight: 500;
        }

        .foreman-note {
            margin-top: 12px;
            padding-top: 10px;
            border-top: 1px dashed var(--border-color);
            font-family: var(--mono-font);
            font-size: 0.85rem;
            font-style: italic;
            color: var(--text-secondary);
        }

        /* Interactive Bridge Rig */
        .beam-rig {
            display: flex;
            align-items: flex-end;
            justify-content: center;
            gap: 4px;
            height: 84px;
            margin-bottom: 10px;
        }

        .rig-pier {
            width: 30px;
            height: 100%;
            background: var(--panel-sunken);
            border: 1px solid var(--border-color);
            border-radius: 2px 2px 0 0;
            display: flex;
            align-items: flex-end;
            justify-content: center;
            font-size: 1.2rem;
            padding-bottom: 2px;
            flex-shrink: 0;
        }

        .gap-zone {
            flex: 1;
            height: 100%;
            border-bottom: 3px dashed var(--accent-amber);
            padding: 6px 6px 6px;
            display: flex;
            align-items: flex-end;
        }

        .gap-track {
            width: 100%;
            min-height: 48px;
            display: flex;
            align-items: center;
            gap: 4px;
            flex-wrap: wrap;
            border: 2px dashed var(--border-color);
            border-radius: 6px;
            background: var(--panel-sunken);
            padding: 6px;
            transition: border-color 0.2s ease, background-color 0.2s ease;
        }

        .gap-track:empty::before {
            content: "⬅ drag beam segments here";
            font-family: var(--mono-font);
            font-size: 0.8rem;
            color: var(--text-secondary);
            font-style: italic;
            padding: 4px;
        }

        .gap-track.drop-hover {
            border-color: var(--accent-blue);
            background: var(--kit-accent-glow);
        }

        /* Load Meter */
        .fill-meter {
            position: relative;
            width: 100%;
            height: 16px;
            background: var(--panel-sunken);
            border: 1px solid var(--border-color);
            border-radius: 8px;
            margin-bottom: 8px;
            overflow: hidden;
        }

        .fill-bar-inner {
            height: 100%;
            width: 0%;
            background: var(--accent-blue);
            border-radius: 8px 0 0 8px;
            transition: width 0.25s ease, background-color 0.25s ease;
        }

        .fill-bar-inner.over-target {
            background: var(--accent-red);
        }

        .fill-bar-inner.exact-target {
            background: var(--accent-green);
        }

        .target-tick {
            position: absolute;
            top: -2px;
            bottom: -2px;
            left: 66.667%;
            width: 3px;
            background: var(--accent-amber);
        }

        .readout-row {
            display: flex;
            justify-content: space-between;
            flex-wrap: wrap;
            gap: 10px;
            margin-bottom: 18px;
            font-family: var(--mono-font);
            font-size: 0.85rem;
        }

        .readout-chip {
            background: var(--panel-bg);
            border: 1px solid var(--border-color);
            border-radius: 4px;
            padding: 6px 12px;
            font-weight: 700;
        }

        /* Supply Yard */
        .panel-label {
            font-family: var(--mono-font);
            font-size: 0.78rem;
            text-transform: uppercase;
            letter-spacing: 0.5px;
            font-weight: 700;
            color: var(--text-secondary);
            margin-bottom: 8px;
        }

        .panel-hint {
            text-transform: none;
            font-weight: 500;
            font-style: italic;
        }

        .supply-yard {
            display: flex;
            flex-wrap: wrap;
            gap: 10px;
            min-height: 60px;
            border: 2px dashed var(--border-color);
            border-radius: 6px;
            background: var(--panel-sunken);
            padding: 10px;
            margin-bottom: 16px;
        }

        .supply-yard.drop-hover {
            border-color: var(--accent-blue);
            background: var(--kit-accent-glow);
        }

        .beam-segment {
            background: var(--container-bg);
            border: 2px solid var(--accent-amber);
            border-radius: 6px;
            padding: 10px 16px;
            font-family: var(--mono-font);
            font-weight: 700;
            font-size: 1rem;
            color: var(--text-primary);
            cursor: grab;
            touch-action: none;
            user-select: none;
            box-shadow: 0 3px 8px var(--shadow-color);
            display: inline-flex;
            align-items: center;
            justify-content: center;
        }

        .beam-segment:active { cursor: grabbing; }

        .beam-segment.dragging {
            opacity: 0.85;
            pointer-events: none;
            box-shadow: 0 8px 18px var(--shadow-color);
            z-index: 5000;
        }

        .beam-segment.locked {
            cursor: default;
            opacity: 0.6;
        }

        .control-row {
            display: flex;
            justify-content: center;
            gap: 12px;
            margin-bottom: 14px;
            flex-wrap: wrap;
        }

        .secondary-btn {
            background: transparent;
            color: var(--text-primary);
            border: 2px solid var(--border-color);
            padding: 12px 22px;
            font-family: var(--display-font);
            font-size: 0.9rem;
            font-weight: 600;
            text-transform: uppercase;
            letter-spacing: 1px;
            cursor: pointer;
            border-radius: 4px;
        }

        .secondary-btn:hover { border-color: var(--accent-blue); }
        .secondary-btn:disabled, .action-btn:disabled { opacity: 0.5; cursor: not-allowed; }

        /* Beam result animations */
        @keyframes holdFirm {
            0%, 100% { transform: translateY(0); }
            30% { transform: translateY(-4px); }
            55% { transform: translateY(1px); }
        }

        @keyframes sagDown {
            0% { transform: translateY(0) rotate(0deg); }
            100% { transform: translateY(10px) rotate(-1deg); }
        }

        @keyframes crackShake {
            0%, 100% { transform: translateX(0); }
            20% { transform: translateX(-6px) rotate(-1deg); }
            40% { transform: translateX(6px) rotate(1deg); }
            60% { transform: translateX(-4px); }
            80% { transform: translateX(4px); }
        }

        .beam-rig.result-hold .gap-track {
            border-color: var(--accent-green);
            border-style: solid;
            animation: holdFirm 0.6s ease;
        }

        .beam-rig.result-under .gap-track {
            border-color: var(--accent-amber);
            animation: sagDown 0.5s ease forwards;
        }

        .beam-rig.result-over .gap-track {
            border-color: var(--accent-red);
            animation: crackShake 0.5s ease;
        }

        .feedback-line {
            font-family: var(--mono-font);
            text-align: center;
            font-size: 0.98rem;
            font-weight: 700;
            min-height: 24px;
        }

        .text-success { color: var(--accent-green); }
        .text-error { color: var(--accent-red); }

        .score-readout {
            font-family: var(--mono-font);
            font-size: 1.15rem;
            background: var(--panel-bg);
            padding: 10px 22px;
            border: 1px solid var(--border-color);
            border-radius: 4px;
            margin-bottom: 12px;
            color: var(--accent-blue);
        }

        footer {
            margin-top: 20px;
            font-family: var(--mono-font);
            font-size: 0.8rem;
            color: var(--text-secondary);
            text-align: center;
        }

        @media (max-width: 640px) {
            .hud-bar { flex-direction: column; align-items: flex-start; }
        }