Pressing button effect

CSS:

.button {
    position: absolute;
} 
#startBtn {
    font-family: OpenSans;
    color: #FFFFFF;
    background-color: #00FF7C;
    border: 1px solid #00FF7C;
    border-radius: 5px;
    box-shadow: 0px 5px 0px #00823F;
    position: relative;
    top: 0px;
    transition: all ease 0.3s;
}
#startBtn:active {
    box-shadow: 0 3px 0 #00823F;
    top: 3px; 
}

HTML

<input id="startBtn" type="button" value="Let's begin" />

Source: http://stackoverflow.com/questions/32459859/css-button-pressing-effect