add fixed button bottom

1#fixed_button{
2    position: fixed;
3    z-index: 999;
4    right: 0.75rem;
5    bottom: 0.75rem;
6    display: none;
7    width: 2.625rem;
8    height: 2.625rem;
9    border-radius: 1.875rem;
10    background: #4f3cda url("../images/up-arrow.png") no-repeat center 47%;
11        background-size: auto;
12    background-size: 1.125rem 1.125rem;
13    text-indent: -9999px;
14}