1 
2<button class="button">
3  hover me
4  <span></span><span></span><span></span><span></span>
5</button>          

 1 
 2.button {
 3  cursor: pointer;
 4  --c: #0ea5e9;
 5  padding: 12px 28px;
 6  margin: 1em;
 7  position: relative;
 8  min-width: 12em;
 9  background: transparent;
10  font-size: 12px;
11  font-weight: bold;
12  color: var(--c);
13  text-align: center;
14  text-transform: uppercase;
15  font-family: sans-serif;
16  letter-spacing: 0.1em;
17  border: 2px solid var(--c);
18  border-radius: 8px;
19  overflow: hidden;
20  z-index: 1;
21  transition: 0.5s;
22}
23 
24.button span {
25  position: absolute;
26  width: 25%;
27  height: 100%;
28  background-color: var(--c);
29  transform: translateY(150%);
30  border-radius: 50%;
31  left: calc((var(--n) - 1) * 25%);
32  transition: 0.5s;
33  transition-delay: calc((var(--n) - 1) * 0.1s);
34  z-index: -1;
35}
36 
37.button:hover {
38  color: black;
39}
40 
41.button:hover span {
42  transform: translateY(0) scale(2);
43}
44 
45.button span:nth-child(1) {
46  --n: 1;
47}
48 
49.button span:nth-child(2) {
50  --n: 2;
51}
52 
53.button span:nth-child(3) {
54  --n: 3;
55}
56 
57.button span:nth-child(4) {
58  --n: 4;
59}