A simple pure CSS hover effect

<button class="btn-thevos001"><span>Hover me!</span></button></div>

.btn-thevos001 {
    border: none;
    display: inline-block;
    text-align: center;
    vertical-align: middle;
    cursor: pointer;
    text-transform: uppercase;
    outline: none;
    overflow: hidden;
    position: relative;
    color: #fff !important;
    font-weight: 700;
    font-size: 15px;
    background-color: #222;
    padding: 17px 60px;
    margin: 0 auto;
    box-shadow: 0 5px 15px rgba(0,0,0,0.20);
    text-decoration: none !important;
}

.btn-thevos001 span {
  position: relative; 
  z-index: 1;
}

.btn-thevos001:after {
    content: "";
    position: absolute;
    left: 0;
    top: 0;
    height: 490%;
    width: 140%;
    background: #10a0e6;
    -webkit-transition: all .5s ease-in-out;
    transition: all .5s ease-in-out;
    -webkit-transform: translateX(-98%) translateY(-25%) rotate(45deg);
    transform: translateX(-98%) translateY(-25%) rotate(45deg);
}

.btn-thevos001:hover:after {
  -webkit-transform: translateX(-9%) translateY(-25%) rotate(45deg);
  transform: translateX(-9%) translateY(-25%) rotate(45deg);
}