* {
    padding: 0;
    margin: 0;
    box-sizing: border-box;
    outline: none;
    border: none;
}

button {
    display: block;
    margin: 100px auto;
    padding: 14px 20px;
    border-radius: 8px;
    background: gray;
    color: #fff;
    cursor: pointer;
    position: relative;
    overflow: hidden;
}

button::before {
    content: "";
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: orangered;
    transform: scale(0);
    transform-origin: bottom right;
    transition: transform 0.4s;
}

button span {
    position: relative;
}

button:hover::before {
    transform: scale(1);
    transform-origin: top left;
}