style.css

body {
    margin: 0;
    padding: 0;
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
}

.container {
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
}

.calculator {
    display: flex;
    flex-direction: column;
    width: 20vw;
    height: 22vw;
    border-radius: 10px;
    background-color: #202020;
}

.display {
    text-align: end;
    height: 15%;
    padding: 10px;
}

.steps {
    color: grey;
    font-size: 14px;
    padding-right: 10px;
    font-weight: 550;
}

.total {
    color: white;
    font-size: 48px;
    font-weight: 550;
}

.buttons {
    display: flex;
    flex-wrap: wrap;
    flex: auto;
    height: 85%;
    gap: 2px;
    margin-bottom: 2px;
    justify-content: center;
    -webkit-user-select: none; /* Safari */
    -ms-user-select: none; /* IE 10 and IE 11 */
    user-select: none; /* Standard syntax */
}

button {
    background-color: #323232;
    color: white;
    display: flex;
    justify-content: center;
    align-items: center;
    border: none;
    border-radius: 5px;
    width: 24%;
    height: 16%;
    font-size: 14px;
    margin: 0;
}

button:hover {
    background-color: #3B3B3B;
}

.number {
    background-color: #3B3B3B;
    font-size: 18px;
}

.number:hover {
    background-color: #323232;
}

#equal {
    background-color: #9FCAB7;
    font-size: 32px;
    color: #323232;
}

#equal:hover {
    background-color: #92B8A8;
}

sup {
    font-size: 10px;
    margin-bottom: 10px;
}

sub {
    margin-top: 5px;
}