main.css

body {
    background-color:#F0F0F0;
    padding: 2em;
    font-family: 'Raleway','Source Sans Pro', 'Arial';
}
.container {
    width: 50%;
    margin: 0 auto;
}
.operation {
    border:1px solid black;
}
div {
    padding:10px;
    margin-bottom: 1em;
    margin-top: 1em;
}
select {
    padding:10px;
    margin-bottom: 1em;
}
label {
    display:block;
    margin-bottom:10px;
}
input {
    padding:10px;
    width: 50%;
    margin-bottom: 1em;
}
button {
    margin: 2em 0;
    padding: 1em 4em;
    display:block;
}
table {
    border: 1px solid #CCC;
    border-collapse: collapse;
    text-align: center;
}

td,tr,th {
    border: none;
    padding-left: 20px;
    margin-left: 20px;
}
#instructor {
    padding:1em;
    background-color:#fff;
    margin: 1em 0;
}