index.css

.card {
    display: inline-block;
    width: 100px;
    height: 100px;
    font-size: 50px;
    padding: 15px;
    text-align: center;
    vertical-align: center;
    margin: 10px;
    border: 1px solid black;
}

#main {
    display: inline-block;
}

#operators {
    display: inline-block;
    vertical-align: top;
}

#operators .card {
    display: block;
    vertical-align: middle;
    height: 77px;
    width: 77px;
    padding: 10px;
    margin: 10px;
}

#input {
    display: block;
    margin-top: 50px;
    font-size: 50px;
    border-top: none;
    border-left: none;
    border-right: none;
    border-bottom: 2px solid black;
}

#dashboard {
    display: inline-block;
}

#timer {
    display: inline-block;
    vertical-align: top;
    margin-left: 50px;
    font-size: 70px;
}

#title {
    margin-left: 10px;
    font-size: 80px;
    font-weight: bold;
}

#result {
    vertical-align: bottom;
}