/* Reset and base styles */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

:root {
    /* Colors */
    --primary-bg: #ffffff;
    --secondary-bg: #f5f7fa;
    --border-color: #d1d9e6;
    --text-primary: #2d3748;
    --text-secondary: #4a5568;
    --text-muted: #718096;

    /* PID term colors */
    --p-color: #3b82f6;
    --i-color: #10b981;
    --d-color: #ef4444;

    /* Spacing */
    --spacing-xs: 0.25rem;
    --spacing-sm: 0.5rem;
    --spacing-md: 1rem;
    --spacing-lg: 1.5rem;
    --spacing-xl: 2rem;

    /* Typography */
    --font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, sans-serif;
    --font-size-sm: 0.875rem;
    --font-size-base: 1rem;
    --font-size-lg: 1.125rem;
    --font-size-xl: 1.25rem;
    --font-size-2xl: 1.5rem;

    /* Layout */
    --side-panel-width: 40%;
}

body {
    font-family: var(--font-family);
    font-size: var(--font-size-base);
    color: var(--text-primary);
    background: var(--secondary-bg);
    line-height: 1.6;
}

.app-container {
    display: flex;
    min-height: 100vh;
    max-width: 1600px;
    margin: 0 auto;
    background: var(--primary-bg);
}

/* Draggable divider between main content and side panel */
.resize-handle {
    width: 6px;
    cursor: col-resize;
    background: var(--border-color);
    flex-shrink: 0;
    position: relative;
    transition: background 0.2s;
}

.resize-handle:hover,
.resize-handle.dragging {
    background: var(--p-color);
}

.resize-handle::after {
    content: '';
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    width: 2px;
    height: 32px;
    background: rgba(0, 0, 0, 0.2);
    border-radius: 1px;
}

.main-content {
    flex: 1;
    min-width: 0;
    padding: var(--spacing-xl);
    overflow-y: auto;
}

/* Header */
.app-header {
    margin-bottom: var(--spacing-xl);
    padding-bottom: var(--spacing-lg);
    border-bottom: 2px solid var(--border-color);
}

.app-header h1 {
    font-size: var(--font-size-2xl);
    font-weight: 600;
    margin-bottom: var(--spacing-md);
    color: var(--text-primary);
}

.equation-display {
    display: flex;
    align-items: center;
    gap: var(--spacing-md);
    padding: var(--spacing-md);
    background: var(--secondary-bg);
    border-radius: 8px;
    margin-bottom: var(--spacing-sm);
}

.equation-label {
    font-weight: 600;
    color: var(--text-secondary);
}

.equation {
    font-size: var(--font-size-lg);
    font-family: 'Courier New', monospace;
}

.equation .term {
    cursor: pointer;
    padding: 2px 4px;
    border-radius: 4px;
    transition: background 0.2s;
}

.equation .term:hover {
    background: rgba(0, 0, 0, 0.05);
}

.equation .p-term {
    color: var(--p-color);
    font-weight: 600;
}

.equation .i-term {
    color: var(--i-color);
    font-weight: 600;
}

.equation .d-term {
    color: var(--d-color);
    font-weight: 600;
}

.equation-hint {
    font-size: var(--font-size-sm);
    color: var(--text-muted);
    font-style: italic;
}

.system-description {
    font-size: var(--font-size-sm);
    color: var(--text-secondary);
    margin-top: var(--spacing-xs);
}

/* Sections */
section {
    margin-bottom: var(--spacing-xl);
}

section h3 {
    font-size: var(--font-size-xl);
    font-weight: 600;
    margin-bottom: var(--spacing-md);
    color: var(--text-secondary);
}

/* Simulation section */
.simulation-section {
    background: var(--secondary-bg);
    border-radius: 8px;
    padding: var(--spacing-lg);
}

#simulation-canvas {
    display: block;
    width: 100%;
    height: auto;
    border: 2px solid var(--border-color);
    border-radius: 4px;
    background: white;
    margin-bottom: var(--spacing-md);
}

.sim-controls {
    display: grid;
    grid-template-columns: 1fr 1fr auto;
    align-items: center;
    gap: var(--spacing-lg);
}

.sim-control-group {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-xs);
}

.sim-control-group label {
    font-weight: 500;
    white-space: nowrap;
}

#target-value {
    display: inline-block;
    min-width: 2rem;
    font-weight: 600;
    color: #f59e0b;
}

#gravity-value {
    display: inline-block;
    min-width: 2rem;
    font-weight: 600;
    color: var(--text-secondary);
}

/* Controls section */
.controls-section {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-lg);
}

.pid-controls {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: var(--spacing-lg);
}

.control-group label {
    display: block;
    margin-bottom: var(--spacing-sm);
    font-weight: 500;
}

.control-hint {
    font-size: var(--font-size-sm);
    color: var(--text-muted);
    font-style: italic;
    margin-left: var(--spacing-sm);
}

.preset-controls {
    display: flex;
    flex-wrap: wrap;
    align-items: center;
    gap: var(--spacing-sm);
}

.preset-controls label {
    font-weight: 600;
    color: var(--text-secondary);
}

.action-controls {
    display: flex;
    gap: var(--spacing-md);
}

/* Metrics section */
.metrics-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: var(--spacing-md);
}

.metric {
    padding: var(--spacing-md);
    background: var(--secondary-bg);
    border-radius: 8px;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.metric-label {
    font-weight: 500;
    color: var(--text-secondary);
    cursor: pointer;
}

.metric-label:hover {
    text-decoration: underline;
}

.metric-value {
    font-size: var(--font-size-lg);
    font-weight: 600;
    color: var(--text-primary);
}

/* Graphs section */
.graphs-section {
    display: grid;
    grid-template-columns: 1fr;
    gap: var(--spacing-lg);
}

.graph-container {
    background: var(--primary-bg);
    border: 1px solid var(--border-color);
    border-radius: 8px;
    padding: var(--spacing-md);
}

/* Responsive design */
@media (max-width: 1024px) {
    .app-container {
        flex-direction: column;
    }

    .resize-handle {
        display: none;
    }

    .side-panel {
        position: fixed;
        right: -100%;
        top: 0;
        bottom: 0;
        width: 320px;
        transition: right 0.3s ease;
        z-index: 1000;
    }

    .side-panel.open {
        right: 0;
    }
}

@media (max-width: 768px) {
    .main-content {
        padding: var(--spacing-md);
    }

    .app-header h1 {
        font-size: var(--font-size-xl);
    }

    .equation-display {
        flex-direction: column;
        align-items: flex-start;
    }

    .equation {
        font-size: var(--font-size-base);
    }

    .pid-controls {
        grid-template-columns: 1fr;
    }

    .sim-controls {
        grid-template-columns: 1fr;
    }

    .action-controls {
        flex-direction: column;
    }

    .side-panel {
        top: auto;
        bottom: -100%;
        right: 0;
        left: 0;
        width: 100%;
        height: 60vh;
        transition: bottom 0.3s ease;
    }

    .side-panel.open {
        bottom: 0;
    }

    .graphs-section {
        gap: var(--spacing-md);
    }
}