:root {
    /* Monochrome palette */
    --bg-primary: #000000; /* Black background */
    --bg-secondary: #1a1a1a; /* Dark gray container background */
    --text-primary: #ffffff; /* White text */
    --text-secondary: #cccccc; /* Light gray text */
    --shadow-soft: 0 10px 25px rgba(255, 255, 255, 0.05);
    --shadow-medium: 0 20px 40px rgba(255, 255, 255, 0.1);
    --border-radius: 20px;
    --border-radius-small: 12px;
    --transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

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

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
    background: var(--bg-primary);
    color: var(--text-primary);
    min-height: 100vh;
    overflow-x: hidden;
}

/* Calculator container */
.calculator-container {
    max-width: 400px;
    width: 100%;
    margin: 0 auto;
    padding: 2rem;
}

.calculator-header {
    text-align: center;
    margin-bottom: 2rem;
}

.calculator-title {
    color: var(--text-primary);
    font-weight: 600;
    font-size: 2rem;
    text-shadow: none; /* Remove shadow for cleaner look */
    margin: 0;
}

/* Main calculator */
.calculator {
    background: var(--bg-secondary);
    border-radius: var(--border-radius);
    padding: 2rem;
    box-shadow: var(--shadow-medium);
    backdrop-filter: none; /* Remove blur */
    border: 1px solid rgba(255, 255, 255, 0.1);
}

/* Display styles */
.display-container {
    background: #333333; /* dark gray */
    border-radius: var(--border-radius-small);
    padding: 1.5rem;
    margin-bottom: 1.5rem;
    border: 1px solid rgba(255, 255, 255, 0.1);
    min-height: 80px;
    display: flex;
    flex-direction: column;
    justify-content: center;
}

.display-secondary {
    font-size: 0.875rem;
    color: var(--text-secondary);
    text-align: right;
    margin-bottom: 0.25rem;
    min-height: 1rem;
    font-weight: 400;
}

.display-primary {
    font-size: 2rem;
    font-weight: 600;
    color: var(--text-primary);
    text-align: right;
    word-break: break-all;
    transition: var(--transition);
}

/* Button grid */
.button-grid {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 0.75rem;
}

/* Base button styles */
.btn {
    border: none;
    border-radius: var(--border-radius-small);
    font-size: 1.125rem;
    font-weight: 500;
    height: 60px;
    transition: var(--transition);
    cursor: pointer;
    position: relative;
    overflow: hidden;
    font-family: inherit;
    display: flex;
    align-items: center;
    justify-content: center;
    box-shadow: 0 4px 12px rgba(255, 255, 255, 0.05);
    background: #222222;
    color: var(--text-primary);
}

.btn:before {
    content: '';
    position: absolute;
    top: 0;
    left: -100%;
    width: 100%;
    height: 100%;
    background: linear-gradient(90deg, transparent, rgba(255, 255, 255, 0.15), transparent);
    transition: var(--transition);
}

.btn:hover:before {
    left: 100%;
}

.btn:active {
    transform: scale(0.95);
}

/* Number buttons */
.btn-number {
    background: #222222;
    color: var(--text-primary);
    border: 1px solid rgba(255, 255, 255, 0.1);
}

.btn-number:hover {
    background: #444444;
    transform: translateY(-2px);
    box-shadow: 0 8px 20px rgba(255, 255, 255, 0.1);
}

/* Zero button spans two columns */
.btn-zero {
    grid-column: span 2;
}

/* Operator buttons */
.btn-operator {
    background: #ffffff; /* White buttons */
    color: #000000; /* Black text */
    font-weight: 600;
    border: 1px solid #ccc;
}

.btn-operator:hover {
    background: #e6e6e6;
    box-shadow: 0 8px 20px rgba(0, 0, 0, 0.15);
    transform: translateY(-2px);
}

/* Function buttons (AC, C, backspace) */
.btn-function {
    background: #ffffff;
    color: #000000;
    font-weight: 600;
    border: 1px solid #ccc;
}

.btn-function:hover {
    background: #e6e6e6;
    box-shadow: 0 8px 20px rgba(0, 0, 0, 0.15);
    transform: translateY(-2px);
}

/* Equals button */
.btn-equals {
    background: var(--text-primary); /* White text-primary is #fff, but we want black for bg */
    background: #000000; /* Black bg */
    color: #ffffff;
    font-weight: 600;
    font-size: 1.5rem;
    border: 1px solid #444;
}

.btn-equals:hover {
    background: #222222;
    box-shadow: 0 8px 20px rgba(255, 255, 255, 0.2);
    transform: translateY(-2px);
}

/* Footer */
.calculator-footer {
    text-align: center;
    margin-top: 1.5rem;
    color: #ffffff;
}

.calculator-footer small {
    color: rgb(255, 255, 255);
    font-size: 0.75rem;
}

/* Active state animation */
.btn-active {
    animation: pulse 0.2s ease-in-out;
}

@keyframes pulse {
    0% { transform: scale(1); }
    50% { transform: scale(0.95); }
    100% { transform: scale(1); }
}

/* Error state */
.display-error {
    color: #ff4c4c !important;
    animation: shake 0.5s ease-in-out;
}

@keyframes shake {
    0%, 100% { transform: translateX(0); }
    25% { transform: translateX(-5px); }
    75% { transform: translateX(5px); }
}

/* Responsive design */
@media (max-width: 480px) {
    .calculator-container {
        padding: 1rem;
    }
    
    .calculator {
        padding: 1.5rem;
    }
    
    .calculator-title {
        font-size: 1.5rem;
    }
    
    .display-primary {
        font-size: 1.75rem;
    }
    
    .btn {
        height: 55px;
        font-size: 1rem;
    }
    
    .btn-equals {
        font-size: 1.25rem;
    }
}

@media (max-width: 360px) {
    .button-grid {
        gap: 0.5rem;
    }
    
    .btn {
        height: 50px;
        font-size: 0.875rem;
    }
    
    .display-primary {
        font-size: 1.5rem;
    }
}

/* Accessibility improvements */
.btn:focus {
    outline: 2px solid #ffffff;
    outline-offset: 2px;
}

@media (prefers-reduced-motion: reduce) {
    * {
        animation-duration: 0.01ms !important;
        animation-iteration-count: 1 !important;
        transition-duration: 0.01ms !important;
    }
}