style.css

.slide {

    border: 2px solid #fffc00;
    color: #4fec51;
    position: relative;
    overflow: hidden;
    z-index: 1;
    transition: .5s;

}

.slide::before {
    content: "";
    position: absolute;
    z-index: -1;
    width: 100%;
    height: 100%;
    left: 0;
    background-color: #fffc00;
    transition: ease-in-out .5s;
}

.slide:hover::before {
    width: 0;
}
#b_1{
    background-color: #4CAF50;
}