style.css

*{
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}
body{
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    background-color: black;
}
.btn{
    width: 10rem;
    height: 4rem;
    position: relative;
    display: flex;
    justify-content: center;
    align-items: center;
    position: relative;
}
.btn button{
    position: absolute;
    width: 100%;
    height: 100%;
    border: none;
    background: rgba(255, 255, 255, 0);
    backdrop-filter: blur(20px);
    color: rgba(0, 0, 0, 0.884);
    cursor: pointer;
    font-size: .95em;
    transition: all .4s;
    border-radius: 20px;
}
.btn button:hover{
    color: white;
}
.element,.elements{
    content: '';
    position: absolute;
    top: 10%;
    left: -1.5%;
    width: 100%;
    height: 100%;
    background: none;
    z-index: -2;
    border: 5px solid  violet;
    border-radius: 20px;
    transition: all .4s;
}
.btn button:hover ~ .element{
    background: gold;
    border: 5px solid  gold;
    top: -10%;
    left: 1.5%;
}