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

body {
    height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    font-family: Arial, sans-serif;
    background: #111827;
}

.calculator {
    width: 480px;
    background: #E5E7EB;
    border-radius: 16px;
    padding: 20px;
    box-shadow: 0 12px 30px rgba(0,0,0,0.3);
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 12px;
}

 .display-container {
    grid-column: span 4;
    background: #111827;
    padding: 12px;
    border-radius: 10px;
}

#history {
    font-size: 14px;
    color: #9ca3af;
    text-align: right;
    min-height: 20px;
    opacity: 0.7;
}

#display {
    font-size: 36px;
    color: #f9fafb;
    text-align: right;
    overflow: hidden;
    white-space: nowrap;
}

#display.error {
    font-size: 24px;
    padding: 7px 0;
    color: #ff4d4d;
}

button {
    padding: 18px;
    font-size: 18px;
    border: none;
    border-radius: 10px;
    cursor: pointer;
}

.number {
    background: #374151;
    color: #FFFFFF;
}

.number:hover {
    background: #4b5563;
}

.operator {
    background: #3882F6;
    color: #FFFFFF;
}

.operator:hover {
    background: #2563EB;
}

#equals {
    background: #10B981;
    color: #FFFFFF;
    grid-column: span 2;
}

#equals:hover {
    background: #059669;
}

.clear {
    background: #eF4444;
    color: #FFFFFF;
}

.clear:hover {
    background: #DC2626;
}

.backspace {
    background: #F59E0B;
    color: #FFFFFF;
    grid-column: span 2;
}

.backspace:hover {
    background: #D97706;
}

#decimal {
    background: #6B7280;
    color: #FFFFFF;
}

#decimal:hover {
    background: #4B5563;
}