body{
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    background-color: #f4f4f9;
    font-family: Arial, Sans-Serif;
    margin: 0;
}

.calculator{
    background-color: #333;
    padding: 20px;
    border-radius: 10px;
    box-shadow: 0px 4px 15px rgba(0, 0, 0, 0.2);
    width: 300px;
}

#display{
    width: 100%;
    height: 50px;
    background-color: #222;
    color: #00ff00;
    text-align: right;
    font-size: 24px;
    border: none;
    border-radius: 5px;
    padding: 10px;
    box-sizing: border-box;
    margin-bottom: 20px;
}

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

button{
    height: 60px;
    background-color: #555;
    color: white;
    border: none;
    border-radius: 5px;
    font-size: 20px;
    cursor: pointer;
    transition: background-color 0.2s;
}

button:hover{
    background-color: #777;
}

button:active{
    background-color: #999;
}

.operator{
    background-color: #ff9500;
}

.operator:hover{
    background-color: #ffaa33;
}

.clear{
    background-color: #ff3b30;
    grid-column: span 3;
}

.clear:hover{
    background-color: #ff5c53;
}

.equals{
    background-color: #34c759;
    grid-column: span 2;
}

.equals:hover{
    background-color: #55d877;
}

.zero{
    grid-column: span 1;
}