main {
    width: 10%;
    margin: 100px auto;
}
#button-container {
    height: 420px;
    width: 190px;
    border: 2px solid saddlebrown;
    border-radius: 7px;
    box-shadow: 5px 3px 9px;
    background-color: aquamarine;
}
.button-items {
    padding: 5px;
}
.btn {
    width: 42px;
    padding: 15px;
    background-color: darkolivegreen;
    color: white;
    font-size: medium;
    border-radius: 3px;
    box-shadow: 5px 5px 10px;
}
#display {
    font-size: 18px;
    font-weight: bold;
    padding: 5px;
}

@media screen and (max-width: 688px) {
    main {
        width: 50%;
        margin: 150px auto;
    }
    #display {
        margin-left: 5px;
    }
}