body {
    background-color: #1abc9c;
}
.main {
    margin: auto;
    padding: 30px;
    text-align: center;
    color: white;
    border-style: solid;
    border-color: white;
    font-size: large;
    width: 25%;
}
input[type=checkbox] {
    vertical-align: middle;
    position: relative;
    bottom: 1px;
}
label {
    display: block;
}
.main ul {
    list-style-type: none;
}
input:invalid {
    background-color: pink;
    border-width: 1px;
}