:root {
    --bg-color: #f1f5f9;
    --card-bg: #ffffff;
    --text-main: #0f172a;
    --text-muted: #475569;
    --primary: #4f46e5;
    --primary-light: #eef2ff;
    --accent: #0d9488;
    --danger: #e11d48;
    --border: #e2e8f0;
    --radius: 12px;
    --shadow: 0 4px 6px -1px rgb(0 0 0 / 0.1);
}

.dark-theme {
    --bg-color: #0f172a;
    --card-bg: #1e293b;
    --text-main: #f8fafc;
    --text-muted: #94a3b8;
    --border: #334155;
    --primary-light: rgba(79, 70, 229, 0.1);
}

* { margin: 0; padding: 0; box-sizing: border-box; }
body { font-family: 'Inter', sans-serif; background: var(--bg-color); color: var(--text-main); line-height: 1.6; transition: 0.3s; }
.container { max-width: 1000px; margin: 0 auto; padding: 20px; }

header { text-align: center; padding: 40px 0; background: var(--card-bg); border-bottom: 1px solid var(--border); margin-bottom: 30px; }
header h1 { font-size: 2.2rem; color: var(--primary); }
.subtitle { color: var(--text-muted); font-weight: 300; }

.card { background: var(--card-bg); border-radius: var(--radius); padding: 25px; margin-bottom: 25px; box-shadow: var(--shadow); border: 1px solid var(--border); }
h2 { margin-bottom: 15px; font-size: 1.5rem; }

/* Buttons */
button { cursor: pointer; border: none; padding: 10px 18px; border-radius: 8px; font-weight: 600; font-family: inherit; transition: 0.2s; }
.btn-primary { background: var(--primary); color: white; }
.btn-secondary { background: var(--border); color: var(--text-main); }
.btn-accent { background: var(--accent); color: white; }
.btn-danger { background: var(--danger); color: white; }
button:hover { opacity: 0.9; transform: translateY(-1px); }
.w-100 { width: 100%; margin-top: 10px; }

/* Lab Layout */
.lab-layout { display: grid; grid-template-columns: 1fr 280px; gap: 20px; }
@media (max-width: 800px) { .lab-layout { grid-template-columns: 1fr; } }

#map-area { background: white; border: 1px solid var(--border); border-radius: 8px; overflow: hidden; }
svg { width: 100%; height: auto; display: block; }

.side-panel { display: flex; flex-direction: column; gap: 15px; }
.stats-box { background: var(--primary-light); padding: 15px; border-radius: 8px; display: flex; flex-direction: column; gap: 10px; }
.stat-item { display: flex; justify-content: space-between; font-weight: 600; }
.info-bubble { padding: 15px; background: #fffbeb; border: 1px solid #fde68a; border-radius: 8px; font-size: 0.9rem; color: #92400e; min-height: 80px; }

/* Land & Bridges */
.land { fill: #cbd5e1; stroke: #64748b; stroke-width: 2; cursor: pointer; }
.land:hover { fill: #94a3b8; }
.land.active { fill: var(--primary); stroke: white; stroke-width: 3; }
.bridge { stroke: #64748b; stroke-width: 10; stroke-linecap: round; cursor: pointer; transition: 0.3s; }
.bridge.crossed { stroke: #f59e0b; }
.label { fill: #1e293b; font-weight: 700; font-size: 14px; pointer-events: none; text-anchor: middle; }

/* Analysis */
.hidden-section { display: none; }
.analysis-grid { display: grid; grid-template-columns: 1.2fr 1fr; gap: 20px; margin-top: 20px; }
table { width: 100%; border-collapse: collapse; font-size: 0.9rem; }
th, td { padding: 8px; border-bottom: 1px solid var(--border); text-align: left; }
.verdict { margin-top: 15px; padding: 12px; border-radius: 6px; font-weight: 700; text-align: center; }
.possible { background: #d1fae5; color: #065f46; }
.impossible { background: #fee2e2; color: #991b1b; }

/* Free Canvas */
.canvas-container { border: 2px dashed var(--border); border-radius: 8px; padding: 15px; }
.canvas-header { display: flex; justify-content: space-between; align-items: center; margin-bottom: 10px; }
#free-canvas { background: #fefefe; cursor: crosshair; }
.node-circle { fill: var(--primary); stroke: white; stroke-width: 2; }
.edge-line { stroke: #94a3b8; stroke-width: 4; stroke-linecap: round; }
.degree-text { fill: white; font-size: 10px; text-anchor: middle; pointer-events: none; }

/* GPS */
.gps-layout { display: grid; grid-template-columns: 1.5fr 1fr; gap: 20px; }
.gps-map-container { background: white; border: 1px solid var(--border); border-radius: 8px; }
.gps-ui { display: flex; flex-direction: column; gap: 10px; }
.input-group { display: flex; flex-direction: column; }
select { padding: 8px; border-radius: 6px; border: 1px solid var(--border); }
.path-msg { padding: 10px; background: var(--primary-light); border-radius: 6px; font-size: 0.85rem; }

/* Challenges */
.challenge-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(220px, 1fr)); gap: 15px; }
.challenge-card { background: var(--bg-color); padding: 15px; border-radius: 8px; border: 1px solid var(--border); }
.challenge-svg-box { background: white; height: 120px; margin-bottom: 10px; border-radius: 4px; }

/* Narrative */
.narrative-section { background: var(--primary-light); font-style: italic; color: var(--text-muted); }
.problem-statement { border-left: 4px solid var(--primary); padding-left: 15px; margin: 15px 0; color: var(--primary); font-weight: 600; }

footer { text-align: center; padding: 40px; color: var(--text-muted); font-size: 0.8rem; }

/* Section header & controls */
.section-header { display: flex; justify-content: space-between; align-items: flex-start; margin-bottom: 20px; gap: 15px; flex-wrap: wrap; }
.controls { display: flex; gap: 10px; flex-shrink: 0; }

/* Key message blockquote */
blockquote.key-message {
    border-left: 4px solid var(--primary);
    margin: 20px 0 0;
    padding: 14px 20px;
    background: var(--primary-light);
    border-radius: 0 8px 8px 0;
    font-style: italic;
    color: var(--primary);
    font-weight: 600;
}

/* Action buttons */
.action-buttons { display: flex; flex-direction: column; gap: 10px; margin-top: auto; }

/* Small text */
.small { font-size: 0.85rem; color: var(--text-muted); margin-top: 4px; }

/* Euler explanation box */
.euler-explanation {
    margin-top: 15px;
    padding: 14px 18px;
    background: var(--primary-light);
    border-radius: 8px;
    font-size: 0.9rem;
    color: var(--text-muted);
    border-left: 4px solid var(--primary);
}

/* Real-world apps grid */
.apps-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(150px, 1fr)); gap: 15px; margin-top: 10px; }
.app-card {
    display: flex; flex-direction: column; align-items: center; gap: 6px;
    padding: 20px 10px;
    background: var(--bg-color);
    border: 1px solid var(--border);
    border-radius: 10px;
    text-align: center;
    transition: 0.2s;
}
.app-card:hover { transform: translateY(-3px); box-shadow: var(--shadow); }
.app-card span { font-size: 2rem; }
.app-card strong { font-size: 0.95rem; }
.app-card p { font-size: 0.8rem; color: var(--text-muted); margin: 0; }

/* Theme toggle */
.theme-toggle { position: absolute; right: 20px; top: 50%; transform: translateY(-50%); }
header { position: relative; }
#toggleTheme { background: var(--border); font-size: 1.2rem; padding: 8px 12px; border-radius: 8px; }

/* GPS edge weight labels */
#gps-canvas text { font-family: 'Inter', sans-serif; }