style.css

body {
    height: 100vh;
    margin: 0;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;

    background-color: #f6f6f6;

    
}

button {
    border: 2px solid #232323;
}

.container {
    height: 600px;
    width: 350px;
    border: 1px solid black;
    border-radius: 15px;
    background-color: #3e3e3e;

    display: flex;
    flex-direction: column;
    align-items: center;
}

.display {
    display: flex;
    align-items: center;
    justify-content: end;

    margin: 30px 0px;
    padding-right: 20px;
    height: 100px;
    width: 290px;

    border: 1px solid black;
    border-radius: 10px;

    background-color: #9baf52;
    font-size: 32px;
}



.buttons-container {
    display: grid;
    grid-template-columns: 50px 50px 50px 50px;
    grid-template-rows: 50px 50px 50px 50px 50px;

    column-gap: 30px;
    row-gap: 30px;
    
}

.digit, #decimal, .operator[value="+"], .operator[value="-"] {
    background-color: #5b5b5b;
    color: #b8b8b8;
    font-weight: bold;
    font-size: 18px;
}

.operator[value="/"], .operator[value="*"], #clear, #del {
    background-color: #252525;
    color: #b8b8b8;
    font-weight: bold;
    font-size: 18px;
}

button[value="0"] {
    grid-column-start: 1;
    grid-column-end: 3;
}

button[id="equals"] {
    grid-column-start: 4;
    grid-row-start: 4;
    grid-row-end: 6;
    background-color: #a8240a;

    font-weight: bold;
    font-size: 18px;
    color: #b8b8b8;
}

footer {
    display: flex;
}