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

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

.calculator-container {
    text-align: center;
}

h1 {
    color: white;
    margin-bottom: 30px;
    font-size: 2.5em;
    text-shadow: 2px 2px 4px rgba(0, 0, 0, 0.3);
}

.calculator {
    background: white;
    border-radius: 20px;
    padding: 20px;
    box-shadow: 0 20px 60px rgba(0, 0, 0, 0.3);
    width: 320px;
}

.display {
    width: 100%;
    padding: 20px;
    font-size: 2em;
    border: 2px solid #667eea;
    border-radius: 10px;
    margin-bottom: 20px;
    text-align: right;
    background: #f8f9fa;
    color: #333;
    font-weight: bold;
}

.display:focus {
    outline: none;
    border-color: #764ba2;
}

.buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 10px;
}

.btn {
    padding: 20px;
    font-size: 1.2em;
    border: none;
    border-radius: 10px;
    cursor: pointer;
    background: #f0f0f0;
    color: #333;
    font-weight: bold;
    transition: all 0.3s ease;
}

.btn:hover {
    background: #e0e0e0;
    transform: translateY(-2px);
    box-shadow: 0 5px 15px rgba(0, 0, 0, 0.2);
}

.btn:active {
    transform: translateY(0);
    box-shadow: 0 2px 5px rgba(0, 0, 0, 0.1);
}

.btn-operator {
    background: #667eea;
    color: white;
}

.btn-operator:hover {
    background: #5568d3;
}

.btn-equals {
    background: #48bb78;
    color: white;
    grid-column: span 2;
}

.btn-equals:hover {
    background: #38a169;
}

.btn-clear {
    background: #f56565;
    color: white;
}

.btn-clear:hover {
    background: #e53e3e;
}

.btn-delete {
    background: #ed8936;
    color: white;
}

.btn-delete:hover {
    background: #dd6b20;
}

.btn-zero {
    grid-column: span 2;
}

@media (max-width: 480px) {
    .calculator {
        width: 100%;
        max-width: 320px;
    }

    h1 {
        font-size: 2em;
    }

    .display {
        font-size: 1.5em;
    }

    .btn {
        padding: 15px;
        font-size: 1em;
    }
}