1button {
2  padding: 0.8em 1.8em;
3  border: 2px solid #fff;
4  position: relative;
5  overflow: hidden;
6  background-color: #fff;
7  text-align: center;
8  text-transform: uppercase;
9  font-size: 18px;
10  transition: .3s;
11  z-index: 1;
12  font-family: inherit;
13  color: #000;
14  border-radius: 30px;
15  box-shadow: rgba(50, 50, 93, 0.25) 0px 50px 100px -20px, rgba(0, 0, 0, 0.3) 0px 30px 60px -30px, rgba(10, 37, 64, 0.35) 0px -2px 6px 0px inset;
16}
17
18button::after {
19  content: "";
20  width: 0;
21  height: 100%;
22  position: absolute;
23  top: 0;
24  right: 0;
25  background-color: red;
26  text-align: center;
27  display: flex;
28  align-items: center;
29  justify-content: center;
30  transition: all 800ms ease-in-out;
31  z-index: -1;
32  opacity: 80%;
33}
34
35button::before {
36  content: "";
37  width: 0;
38  height: 100%;
39  position: absolute;
40  left: 0;
41  top: 0;
42  background-color: blue;
43  display: flex;
44  align-items: center;
45  justify-content: center;
46  transition: all 800ms ease-in-out;
47  z-index: -1;
48  opacity: 60%;
49}
50
51button:hover::after {
52  width: 37.5%;
53}
54
55button:hover::before {
56  width: 37.5%;
57}