:root {
    --color-primary: #e0e0e0;
    --color-primary-dim: #a0a0a0;
    --color-primary-dark: #606060;
    --color-error: #ff6b6b;
    --color-bg: #0d0d0d;
    --color-bg-card: rgba(20, 20, 20, 0.95);
    --color-border: #2a2a2a;
    --color-text-muted: #888;
    
    --color-accent: #06b6d4;
    --color-accent-dim: rgba(6, 182, 212, 0.2);
    
    --color-success: #22c55e;
    
    --font-sans: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Inter', sans-serif;
    --font-mono: 'JetBrains Mono', 'Fira Code', 'Courier New', monospace;
    
    --shadow-card: 0 4px 12px rgba(0, 0, 0, 0.4);
    --shadow-card-hover: 0 8px 24px rgba(0, 0, 0, 0.5);
    --shadow-input-focus: 0 0 0 2px var(--color-accent-dim);
    
    --transition-default: all 0.3s ease;
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    background: var(--color-bg);
    color: var(--color-primary);
    font-family: var(--font-sans);
    font-size: 16px;
    line-height: 1.6;
    min-height: 100vh;
    position: relative;
}

button, .btn {
    background: rgba(6, 182, 212, 0.1);
    border: 1px solid var(--color-accent);
    color: var(--color-accent);
    padding: 12px 24px;
    font-family: var(--font-mono);
    font-size: 14px;
    text-transform: none;
    letter-spacing: 0.02em;
    cursor: pointer;
    transition: var(--transition-default);
    position: relative;
    overflow: hidden;
}

button:hover, .btn:hover {
    background: rgba(6, 182, 212, 0.2);
    box-shadow: var(--shadow-card-hover);
}

button:active, .btn:active {
    background: rgba(6, 182, 212, 0.3);
}

button:disabled, .btn:disabled {
    opacity: 0.5;
    cursor: not-allowed;
}

input {
    background: #0a0a0a;
    border: 1px solid var(--color-border);
    color: var(--color-primary);
    padding: 12px;
    font-family: var(--font-mono);
    font-size: 14px;
    outline: none;
    transition: var(--transition-default);
}

input:focus {
    border-color: var(--color-accent);
    box-shadow: var(--shadow-input-focus);
}

input::placeholder {
    color: var(--color-primary-dark);
}

label {
    font-size: 13px;
    color: var(--color-primary);
    font-weight: 500;
    letter-spacing: 0.02em;
}

.footer {
    font-size: 12px;
    color: var(--color-text-muted);
    text-align: center;
}

.footer span {
    color: var(--color-accent);
}

.math-symbol {
    font-family: var(--font-sans);
    font-size: 18px;
    opacity: 0.15;
    color: var(--color-accent);
    user-select: none;
    position: absolute;
}

.math-grid {
    position: relative;
}

.math-grid::after {
    content: '';
    position: absolute;
    inset: 0;
    background-image: 
        linear-gradient(rgba(255,255,255,0.02) 1px, transparent 1px),
        linear-gradient(90deg, rgba(255,255,255,0.02) 1px, transparent 1px);
    background-size: 20px 20px;
    pointer-events: none;
    z-index: 0;
}

.uppercase {
    text-transform: uppercase;
}

.letter-spacing-1 {
    letter-spacing: 0.05em;
}

.letter-spacing-2 {
    letter-spacing: 0.1em;
}