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

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

.calculator-container {
    width: 100%;
    max-width: 400px;
}

.calculator {
    background: rgba(255, 255, 255, 0.95);
    border-radius: 20px;
    padding: 20px;
    box-shadow: 0 20px 60px rgba(0, 0, 0, 0.3);
    backdrop-filter: blur(10px);
}

.display {
    background: #1a1a1a;
    color: white;
    padding: 30px 20px;
    border-radius: 15px;
    margin-bottom: 20px;
    text-align: right;
    min-height: 120px;
    display: flex;
    flex-direction: column;
    justify-content: space-between;
}

.previous-operand {
    color: rgba(255, 255, 255, 0.7);
    font-size: 1.2rem;
    min-height: 24px;
    word-wrap: break-word;
    word-break: break-all;
}

.current-operand {
    color: white;
    font-size: 2.5rem;
    font-weight: 600;
    min-height: 40px;
    word-wrap: break-word;
    word-break: break-all;
}

.buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 15px;
}

button {
    padding: 25px;
    font-size: 1.5rem;
    font-weight: 600;
    border: none;
    border-radius: 12px;
    cursor: pointer;
    transition: all 0.2s ease;
    background: #f0f0f0;
    color: #333;
    box-shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
}

button:hover {
    transform: translateY(-2px);
    box-shadow: 0 6px 12px rgba(0, 0, 0, 0.15);
}

button:active {
    transform: translateY(0);
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
}

button[data-operation] {
    background: #667eea;
    color: white;
}

button[data-operation]:hover {
    background: #5568d3;
}

button[data-equals] {
    background: #764ba2;
    color: white;
}

button[data-equals]:hover {
    background: #5d3a7e;
}

button[data-all-clear],
button[data-delete] {
    background: #ff6b6b;
    color: white;
}

button[data-all-clear]:hover,
button[data-delete]:hover {
    background: #ee5a5a;
}

.span-two {
    grid-column: span 2;
}

@media (max-width: 480px) {
    .calculator {
        padding: 15px;
    }
    
    button {
        padding: 20px;
        font-size: 1.3rem;
    }
    
    .current-operand {
        font-size: 2rem;
    }
}