* {
    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;
}

.calculator {
    background: rgba(255, 255, 255, 0.95);
    border-radius: 20px;
    box-shadow: 0 20px 40px rgba(0, 0, 0, 0.3);
    padding: 20px;
    backdrop-filter: blur(10px);
    border: 1px solid rgba(255, 255, 255, 0.2);
}

.display {
    background: #f8f9fa;
    border-radius: 15px;
    padding: 20px;
    margin-bottom: 20px;
    text-align: right;
    min-height: 80px;
    display: flex;
    flex-direction: column;
    justify-content: flex-end;
}

.previous-operand {
    color: #6c757d;
    font-size: 16px;
    margin-bottom: 5px;
    min-height: 20px;
}

.current-operand {
    color: #212529;
    font-size: 36px;
    font-weight: 600;
    overflow: hidden;
    text-overflow: ellipsis;
}

.buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 12px;
}

.btn {
    border: none;
    border-radius: 15px;
    padding: 20px;
    font-size: 20px;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.3s ease;
    background: #ffffff;
    color: #333;
    box-shadow: 0 4px 15px rgba(0, 0, 0, 0.1);
}

.btn:hover {
    transform: translateY(-2px);
    box-shadow: 0 6px 20px rgba(0, 0, 0, 0.15);
}

.btn:active {
    transform: translateY(0);
}

.btn.number {
    background: #ffffff;
    color: #333;
}

.btn.operator {
    background: #e9ecef;
    color: #495057;
}

.btn.equals {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    color: white;
    grid-column: span 2;
}

.btn.equals:hover {
    background: linear-gradient(135deg, #5a6fd8 0%, #6a4190 100%);
}

/* レスポンシブデザイン */
@media (max-width: 480px) {
    .calculator {
        padding: 15px;
        margin: 20px;
    }
    
    .btn {
        padding: 15px;
        font-size: 18px;
    }
    
    .current-operand {
        font-size: 28px;
    }
}