body {
    background-color: #2c3e50;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    margin: 0;
    font-family: Arial, sans-serif;
}

.calculator {
    background-color: #1a1a1a;
    width: 300px;
    padding: 20px;
    border-radius: 15px;
    box-shadow: 0 10px 30px rgba(0,0,0,0.5);
    border: 2px solid #333;
}

.brand {
    color: #4a4a4a;
    font-size: 10px;
    text-align: center;
    margin-bottom: 10px;
}

.display {
    background-color: #9ead86;
    color: #2b2b2b;
    font-family: 'Courier New', Courier, monospace;
    font-size: 32px;
    text-align: right;
    padding: 15px;
    height: 40px;
    margin-bottom: 20px;
    border-radius: 5px;
    border: 4px inset #7c8a6a;
    box-shadow: inset 0 2px 5px rgba(0,0,0,0.5);
}

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

.btn {
    background: #333;
    color: white;
    border: none;
    padding: 15px 0;
    font-size: 18px;
    border-radius: 8px;
    cursor: pointer;
    box-shadow: 0 3px #000;
    transition: all 0.1s;
}

.btn:active {
    box-shadow: 0 1px #000;
    transform: translateY(2px);
}

.clear { background-color: #d35400; }
.operator { background-color: #444; }


.plus-btn {
    grid-row: span 2;
    height: 100%;
}