Belated. If need any fancy button than anyone can try this.
#startStopBtn {_x000D_
font-size: 30px;_x000D_
font-weight: bold;_x000D_
display: inline-block;_x000D_
margin: 0 auto;_x000D_
color: #dcfbb4;_x000D_
background-color: green;_x000D_
border: 0.4em solid #d4f7da;_x000D_
border-radius: 50%;_x000D_
transition: all 0.3s;_x000D_
box-sizing: border-box;_x000D_
width: 4em;_x000D_
height: 4em;_x000D_
line-height: 3em;_x000D_
cursor: pointer;_x000D_
box-shadow: 0 0 0 rgba(0,0,0,0.1), inset 0 0 0 rgba(0,0,0,0.1);_x000D_
text-align: center;_x000D_
}_x000D_
#startStopBtn:hover{_x000D_
box-shadow: 0 0 2em rgba(0,0,0,0.1), inset 0 0 1em rgba(0,0,0,0.1);_x000D_
background-color: #29a074;_x000D_
}
_x000D_
<div id="startStopBtn" onclick="startStop()" class=""> Go!</div>
_x000D_