:root {
    --bg-gradient: linear-gradient(135deg, #f0f2f5 0%, #e2e6ec 100%);
    --glass-bg: rgba(255, 255, 255, 0.7);
    --glass-border: rgba(0, 0, 0, 0.1);
    --text-main: #1e293b;
    --text-muted: #64748b;
    --primary: #0284c7;
    --primary-hover: #0369a1;
    --success: #059669;
    --danger: #dc2626;
    --font-main: 'Outfit', sans-serif;
    --input-bg: rgba(0, 0, 0, 0.06);
    --secondary-btn-bg: rgba(0, 0, 0, 0.08);
    --secondary-btn-hover-bg: rgba(0, 0, 0, 0.14);
    --canvas-bg: rgba(226, 232, 240, 0.85);
    --context-menu-bg: rgba(241, 245, 249, 0.95);
    --feedback-bg: rgba(15, 23, 42, 0.9);
    --panel-shadow: rgba(0, 0, 0, 0.08);
    --scrollbar-thumb: rgba(0, 0, 0, 0.15);
    --scrollbar-thumb-hover: rgba(0, 0, 0, 0.25);
    --menu-item-hover: rgba(0, 0, 0, 0.06);

    /* Semantic force colors — identical in both themes */
    --force-poids: #e74c3c;
    --force-reaction: #2ecc71;
    --force-frottement: #f39c12;
    --force-tension: #3498db;
    --force-electrique: #e67e22;
    --force-default: #3498db;
    --unit-vector: #2ecc71;
    --object-ball: #3498db;
    --object-block: #3498db;
    --object-block-stroke: #2980b9;
    --ground: #2ecc71;
    --slope: #64748b;
    --pivot: #64748b;
    --charged-ball: #f1c40f;
    --plate-pos: #e74c3c;
    --plate-neg: #3498db;
}

:root[data-theme="dark"] {
    --bg-gradient: linear-gradient(135deg, #1a1c2e 0%, #0f172a 100%);
    --glass-bg: rgba(255, 255, 255, 0.05);
    --glass-border: rgba(255, 255, 255, 0.1);
    --text-main: #e2e8f0;
    --text-muted: #94a3b8;
    --primary: #38bdf8;
    --primary-hover: #2980b9;
    --success: #10b981;
    --danger: #ef4444;
    --input-bg: rgba(0, 0, 0, 0.2);
    --secondary-btn-bg: rgba(255, 255, 255, 0.1);
    --secondary-btn-hover-bg: rgba(255, 255, 255, 0.15);
    --canvas-bg: rgba(44, 62, 80, 0.85);
    --context-menu-bg: rgba(30, 41, 59, 0.95);
    --feedback-bg: rgba(15, 23, 42, 0.9);
    --panel-shadow: rgba(0, 0, 0, 0.3);
    --scrollbar-thumb: rgba(255, 255, 255, 0.1);
    --scrollbar-thumb-hover: rgba(255, 255, 255, 0.2);
    --menu-item-hover: rgba(255, 255, 255, 0.1);

    --force-poids: #e74c3c;
    --force-reaction: #2ecc71;
    --force-frottement: #f39c12;
    --force-tension: #3498db;
    --force-electrique: #e67e22;
    --force-default: #3498db;
    --unit-vector: #2ecc71;
    --object-ball: #3498db;
    --object-block: #3498db;
    --object-block-stroke: #2980b9;
    --ground: #2ecc71;
    --slope: #475569;
    --pivot: #7f8c8d;
    --charged-ball: #f1c40f;
    --plate-pos: #e74c3c;
    --plate-neg: #3498db;
}

body {
    margin: 0;
    padding: 0;
    font-family: var(--font-main);
    background: var(--bg-gradient);
    color: var(--text-main);
    display: flex;
    flex-direction: column;
    height: 100vh;
    overflow: hidden;
    transition: background 0.2s ease, color 0.2s ease;
}

#app-container {
    position: relative;
    flex: 1;
    display: flex;
    padding: 16px;
    gap: 16px;
}

#canvas-container {
    flex: 1;
    position: relative;
    background: var(--canvas-bg);
    backdrop-filter: blur(12px);
    border: 1px solid var(--glass-border);
    border-radius: 16px;
    box-shadow: 0 4px 6px -1px var(--panel-shadow);
    overflow: hidden;
    transition: background-color 0.2s ease, border-color 0.2s ease;
}

canvas {
    display: block;
    width: 100%;
    height: 100%;
    cursor: crosshair;
}

#sidebar {
    width: 300px;
    background: var(--glass-bg);
    backdrop-filter: blur(12px);
    border: 1px solid var(--glass-border);
    border-radius: 16px;
    padding: 24px;
    box-shadow: 0 4px 6px -1px var(--panel-shadow);
    display: flex;
    flex-direction: column;
    z-index: 10;
    overflow-y: auto;
    transition: background-color 0.2s ease, border-color 0.2s ease;
}

h1 {
    font-size: 1.25rem;
    font-weight: 700;
    margin-bottom: 24px;
    background: linear-gradient(to right, #0284c7, #6366f1);
    background-clip: text;
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
}

:root[data-theme="dark"] h1 {
    background: linear-gradient(to right, #38bdf8, #818cf8);
    background-clip: text;
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
}

.control-group {
    margin-bottom: 25px;
}

label {
    display: block;
    margin-bottom: 8px;
    font-weight: 500;
    font-size: 0.9rem;
    color: var(--text-muted);
}

select,
button {
    width: 100%;
    padding: 10px;
    border: 1px solid var(--glass-border);
    border-radius: 8px;
    font-family: inherit;
    font-size: 0.9rem;
    background: var(--input-bg);
    color: var(--text-main);
    transition: all 0.2s;
}

select {
    cursor: pointer;
}

select:focus {
    outline: none;
    border-color: var(--primary);
}

button {
    background: var(--primary);
    color: #0f172a;
    border: none;
    font-weight: 600;
    cursor: pointer;
    margin-top: 10px;
}

button:hover {
    transform: translateY(-1px);
    filter: brightness(1.1);
}

button.secondary {
    background: var(--secondary-btn-bg);
    color: var(--text-main);
}

button.secondary:hover {
    background: var(--secondary-btn-hover-bg);
}

button.validate-btn {
    background: var(--success);
    color: #fff;
    margin-top: auto;
}

button.validate-btn:hover {
    background: #059669;
}

.toggle-row {
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-bottom: 15px;
}

.toggle-row label {
    margin-bottom: 0;
}

input[type="checkbox"] {
    accent-color: var(--primary);
    width: 16px;
    height: 16px;
}

#context-menu {
    position: absolute;
    display: none;
    background: var(--context-menu-bg);
    backdrop-filter: blur(10px);
    border: 1px solid var(--glass-border);
    border-radius: 8px;
    box-shadow: 0 4px 15px var(--panel-shadow);
    padding: 5px;
    z-index: 100;
    width: 150px;
    transition: background-color 0.2s ease, border-color 0.2s ease;
}

.menu-item {
    padding: 8px 12px;
    cursor: pointer;
    font-size: 0.9rem;
    color: var(--text-main);
    border-radius: 4px;
    transition: background 0.1s;
}

.menu-item:hover {
    background: var(--menu-item-hover);
}

.menu-item[data-label="delete"] {
    color: var(--danger);
}

.menu-item[data-label="delete"]:hover {
    background: rgba(239, 68, 68, 0.1);
}

#feedback-overlay {
    position: absolute;
    top: 30px;
    left: 50%;
    transform: translateX(-50%);
    background: var(--feedback-bg);
    border: 1px solid var(--glass-border);
    color: #fff;
    padding: 12px 24px;
    border-radius: 30px;
    font-size: 0.95rem;
    pointer-events: none;
    opacity: 0;
    transition: opacity 0.3s;
    backdrop-filter: blur(4px);
    z-index: 50;
    text-align: center;
}

#feedback-overlay.show {
    opacity: 1;
}

#sidebar::-webkit-scrollbar {
    width: 6px;
}

#sidebar::-webkit-scrollbar-track {
    background: transparent;
}

#sidebar::-webkit-scrollbar-thumb {
    background: var(--scrollbar-thumb);
    border-radius: 3px;
}

#sidebar::-webkit-scrollbar-thumb:hover {
    background: var(--scrollbar-thumb-hover);
}

.sidebar-header {
    display: flex;
    align-items: flex-start;
    justify-content: space-between;
    gap: 8px;
    margin-bottom: 24px;
}

.sidebar-header h1 {
    margin-bottom: 0;
}

.sidebar-header .credit {
    font-size: 0.5em;
    font-weight: normal;
    color: var(--text-muted);
    margin-top: 5px;
    display: block;
}

.theme-toggle {
    font-family: var(--font-main);
    font-size: 0.85rem;
    font-weight: 500;
    background: var(--input-bg);
    color: var(--text-main);
    border: 1px solid var(--glass-border);
    border-radius: 8px;
    padding: 6px 10px;
    cursor: pointer;
    flex-shrink: 0;
    transition: background-color 0.2s ease, color 0.2s ease, border-color 0.2s ease;
}

.theme-toggle:hover {
    background: var(--primary);
    color: #fff;
    border-color: var(--primary);
}

.vector-properties {
    background: var(--input-bg);
    padding: 10px;
    border-radius: 8px;
    margin-bottom: 20px;
}

.vector-properties h3 {
    font-size: 0.9rem;
    margin-top: 0;
    margin-bottom: 10px;
    color: var(--primary);
}

.vector-properties .separator {
    border-top: 1px solid var(--glass-border);
    margin: 8px 0;
}

.vector-properties .menu-item[data-label="delete"] {
    color: var(--danger);
}

.instructions-text {
    font-size: 0.85rem;
    color: var(--text-muted);
    line-height: 1.4;
}