#main {
    width: 250px;
    height: 150px;
    text-align: center;

    position: absolute;
    top:0;
    bottom: 0;
    left: 0;
    right: 0;

    margin: auto;
}

.g-signin2 {
    margin-top:10px; margin-left: auto; margin-right: auto; width:120px
}