1.shadow__btn {
2  padding: 10px 20px;
3  border: none;
4  font-size: 17px;
5  color: #fff;
6  border-radius: 7px;
7  letter-spacing: 4px;
8  font-weight: 700;
9  text-transform: uppercase;
10  transition: 0.5s;
11  transition-property: box-shadow;
12}
13
14.shadow__btn {
15  background: rgb(0,140,255);
16  box-shadow: 0 0 25px rgb(0,140,255);
17}
18
19.shadow__btn:hover {
20  box-shadow: 0 0 5px rgb(0,140,255),
21              0 0 25px rgb(0,140,255),
22              0 0 50px rgb(0,140,255),
23              0 0 100px rgb(0,140,255);
24}