:root {
    --bg-primary: #1e1e1e;
    --bg-secondary: #2d2d2d;
    --bg-panel: #333333;
    --text-primary: #e0e0e0;
    --accent: #4a90e2;
    --accent-hover: #357abd;
    --border: #444;
    --shadow: 0 4px 12px rgba(0,0,0,0.5);
}

* { box-sizing: border-box; margin: 0; padding: 0; }
body {
    font-family: 'Segoe UI', system-ui, -apple-system, sans-serif;
    background: var(--bg-primary);
    color: var(--text-primary);
    height: 100vh;
    display: flex;
    flex-direction: column;
    overflow: hidden;
}

/* 顶部导航 */
.app-header {
    background: var(--bg-secondary);
    padding: 10px 20px;
    display: flex;
    justify-content: space-between;
    align-items: center;
    border-bottom: 1px solid var(--border);
    flex-shrink: 0;
    position: relative;
}
.app-header h1 { font-size: 1.1rem; font-weight: 500; }
.header-actions { display: flex; gap: 10px; align-items: center; }

/* 返回首页按钮 */
.back-home-btn {
    display: flex;
    align-items: center;
    gap: 6px;
    background: rgba(74, 144, 226, 0.15);
    color: var(--accent);
    text-decoration: none;
    padding: 6px 14px;
    border-radius: 20px;
    font-size: 0.85rem;
    font-weight: 500;
    transition: all 0.3s ease;
    border: 1px solid rgba(74, 144, 226, 0.3);
}
.back-home-btn:hover {
    background: rgba(74, 144, 226, 0.25);
    transform: translateY(-2px);
    box-shadow: 0 4px 12px rgba(74, 144, 226, 0.3);
}
.back-icon {
    font-size: 1rem;
}

button, .file-upload {
    background: var(--bg-panel);
    color: var(--text-primary);
    border: 1px solid var(--border);
    padding: 6px 12px;
    border-radius: 4px;
    cursor: pointer;
    font-size: 0.85rem;
    transition: all 0.2s;
}
button:hover, .file-upload:hover { background: var(--accent); border-color: var(--accent); }
.file-upload input { display: none; }

/* 主布局 */
.app-main {
    display: grid;
    grid-template-columns: 160px 1fr 200px;
    flex: 1;
    overflow: hidden;
}

.toolbar, .filter-panel {
    background: var(--bg-secondary);
    padding: 15px;
    display: flex;
    flex-direction: column;
    gap: 15px;
}
.toolbar { border-right: 1px solid var(--border); }
.filter-panel { border-left: 1px solid var(--border); }

.tool-btn { width: 100%; text-align: left; }
.tool-btn.active { background: var(--accent); border-color: var(--accent); }

.tool-settings { margin-top: auto; display: flex; flex-direction: column; gap: 10px; }
.tool-settings label, .filter-control label {
    font-size: 0.8rem;
    display: flex;
    flex-direction: column;
    gap: 4px;
    color: var(--text-primary);
}
input[type="range"] { width: 100%; accent-color: var(--accent); }
input[type="color"] { width: 100%; height: 30px; border: none; cursor: pointer; }

/* 画布区域 */
.canvas-wrapper {
    background: #111;
    display: flex;
    justify-content: center;
    align-items: center;
    overflow: auto;
    padding: 20px;
}
canvas {
    background: #ffffff;
    box-shadow: var(--shadow);
    cursor: crosshair;
    display: block;
}

/* 响应式适配 */
@media (max-width: 900px) {
    .app-main {
        grid-template-columns: 1fr;
        grid-template-rows: auto 1fr auto;
    }
    .toolbar, .filter-panel {
        border: none;
        flex-direction: row;
        flex-wrap: wrap;
        padding: 10px;
        gap: 8px;
    }
    .toolbar { border-bottom: 1px solid var(--border); }
    .filter-panel { border-top: 1px solid var(--border); }
    /* 移动端返回首页按钮调整 */
    .back-home-btn {
        padding: 5px 10px;
        font-size: 0.8rem;
    }
    .back-text {
        display: none;
    }
}