body {
    margin: 0;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    background-color: #222222;
    background-image: url(./media/background.jpg);
    background-repeat: no-repeat;
    background-attachment: fixed;
    background-position: center;
}

#keys {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 10px;
    padding: 25px;
}

#calculator {
    font-family: Arial, Helvetica, sans-serif;
    background-color: hsl(0, 0%, 15%);
    border: 10px solid black;
    border-radius: 15px;
    max-width: 500px;
    overflow: hidden;
    align-items: center;
}

#display {
    width: 100%;
    padding: 20px;
    font-size: 5rem;
    text-align: left;
    border: none;
    border-bottom: 5px solid black;
    background-color: hsl(0, 0%, 20%);
    color: white;
}

button {
    width: 100px;
    height: 100px;
    border-radius: 50px;
    border: none;
    background-color: darkslategray;
    color: white;
    font-size: 3rem;
    font-weight: bold;
    cursor: pointer;
}

button:hover {
    background-color: darkorange;
}

button:active {
    background-color: gray;
}

.operator {
    background-color: darkgreen;
}

.operator:hover {
    background-color: darkred;
}

.operator:active {
    background-color: hsl(0, 0%, 35%);
}

#clear {
    display: flex;
    width: 100%;
    justify-content: center;
    padding: 15px;
    padding-top: 0;
    box-sizing: border-box;
}

#clear button {
    width: 90%;
    height: 80px;
    font-size: 2.5rem;
    color: white;
    border-radius: 10px;
    cursor: pointer;
    font-weight: bold;
}

@media (max-width: 768px) {
    button {
        width: 70px;
        height: 70px;
        font-size: 2rem;
    }

    #display {
        font-size: 3rem;
    }
}