#problem,
#answer {
    width: 200px;
    text-align: right;
    border-bottom: solid white 1px;
}

#answer {
    height: auto;
    font-size: 1em;
    text-align: right;
    background: grey;
    border: 0;
}

#problem {
    margin: auto;
}

#mainDisplay {
    background: black;
    width: 100vw;
    height: 100vh;
    margin: auto;
}

#header {
    color: #50ff00;
    text-shadow: 0px 0px 1px #50ff00;
    text-align: center;
    font-size: 5em;
}

#maths {
    color: #ff6565;
    text-shadow: 0px 0px 1px #50ff00;
    text-align: center;
    font-size: 4em;
}

button {
    border: 0;
    background: #f7ff00;
    width: 100%;
    font-size: 5em;
    padding: 0.5em 0;
}

#buttons {
    bottom: 0;
    position: absolute;
    display: block;
    width: 100%;
}

.row {
    width: 100%;
    margin-bottom: 10px;
}

* {
    margin: 0;
}