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

body {
    font-family: 'Roboto', sans-serif;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    min-height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    padding: 20px;
}

.container {
    max-width: 800px;
    width: 100%;
    background: rgba(255, 255, 255, 0.95);
    border-radius: 20px;
    box-shadow: 0 20px 60px rgba(0, 0, 0, 0.3);
    overflow: hidden;
    padding: 30px;
}
/* Header styles */
header {
    text-align: center;
    margin-bottom: 30px;
    padding-bottom: 20px;
    border-bottom: 2px solid #f0f0f0;
}

header h1 {
    color: #333;
    font-size: 2.5rem;
    font-weight: 700;
    margin-bottom: 10px;
}

header h1 i {
    color: #667eea;
    margin-right: 15px;
}

.subtitle {
    color: #666;
    font-size: 1.1rem;
    font-weight: 300;
}
/* Calculator styles */
.calculator {
    background: white;
    border-radius: 15px;
    padding: 25px;
    box-shadow: 0 10px 30px rgba(0, 0, 0, 0.1);
}

.display-container {
    background: #f8f9fa;
    border-radius: 10px;
    padding: 20px;
    margin-bottom: 25px;
    border: 2px solid #e9ecef;
    text-align: right;
    min-height: 120px;
    display: flex;
    flex-direction: column;
    justify-content: flex-end;
}

.expression {
    font-size: 1.2rem;
    color: #6c757d;
    min-height: 30px;
    margin-bottom: 10px;
    word-break: break-all;
}

.display {
    font-size: 3rem;
    font-weight: 500;
    color: #333;
    word-break: break-all;
    line-height: 1.2;
}
/* Buttons grid */
.buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 15px;
    margin-bottom: 30px;
}

.btn {
    border: none;
    border-radius: 10px;
    font-size: 1.5rem;
    font-weight: 500;
    padding: 20px 10px;
    cursor: pointer;
    transition: all 0.2s ease;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 70px;
}

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

.btn:hover {
    filter: brightness(0.9);
}
/* Button types */
.number {
    background: #f8f9fa;
    color: #333;
    border: 2px solid #e9ecef;
}

.number:hover {
    background: #e9ecef;
    border-color: #dee2e6;
}

.zero {
    grid-column: span 2;
}

.operator {
    background: #667eea;
    color: white;
    border: 2px solid #5a6fd8;
}

.operator:hover {
    background: #5a6fd8;
}

.equals {
    background: #28a745;
    color: white;
    border: 2px solid #218838;
}

.equals:hover {
    background: #218838;
}

.decimal {
    background: #ffc107;
    color: #333;
    border: 2px solid #e0a800;
}

.decimal:hover {
    background: #e0a800;
}
/* Instructions */
.instructions {
    background: #f8f9fa;
    border-radius: 10px;
    padding: 20px;
    border-left: 5px solid #667eea;
}

.instructions h3 {
    color: #333;
    margin-bottom: 15px;
    font-size: 1.3rem;
}

.instructions h3 i {
    color: #667eea;
    margin-right: 10px;
}

.instructions ul {
    list-style-type: none;
    padding-left: 0;
}

.instructions li {
    padding: 8px 0;
    color: #555;
    border-bottom: 1px solid #e9ecef;
}

.instructions li:last-child {
    border-bottom: none;
}

.instructions strong {
    color: #333;
    font-weight: 600;
}

/* Footer */
footer {
    text-align: center;
    margin-top: 30px;
    padding-top: 20px;
    border-top: 2px solid #f0f0f0;
    color: #666;
    font-size: 0.9rem;
}
/* Responsive design */
@media (max-width: 768px) {
    .container {
        padding: 20px;
    }
    
    header h1 {
        font-size: 2rem;
    }
    
    .display {
        font-size: 2.5rem;
    }
    
    .btn {
        height: 60px;
        font-size: 1.3rem;
        padding: 15px 5px;
    }
    
    .buttons {
        gap: 10px;
    }
}

@media (max-width: 480px) {
    body {
        padding: 10px;
    }
    
    .container {
        padding: 15px;
    }
    
    header h1 {
        font-size: 1.7rem;
    }
    
    .display {
        font-size: 2rem;
    }
    
    .btn {
        height: 50px;
        font-size: 1.1rem;
        padding: 10px 5px;
    }
    
    .buttons {
        gap: 8px;
    }
    
    .instructions h3 {
        font-size: 1.1rem;
    }
}