.FlexibleCSS3ButtonInner {
overflow: hidden;
-webkit-border-radius: 40px;
-moz-border-radius: 40px;
border-radius: 40px;
position: relative;
display: block;
height: 40px;
background: rgb(143,200,0);
background: url(data:image/svg+xml;base64,PD94bWwgdmVyc2lvbj0iMS4wIiA/Pgo8c3ZnIHhtbG5zPSJodHRwOi8vd3d3LnczLm9yZy8yMDAwL3N2ZyIgd2lkdGg9IjEwMCUiIGhlaWdodD0iMTAwJSIgdmlld0JveD0iMCAwIDEgMSIgcHJlc2VydmVBc3BlY3RSYXRpbz0ibm9uZSI+CiAgPGxpbmVhckdyYWRpZW50IGlkPSJncmFkLXVjZ2ctZ2VuZXJhdGVkIiBncmFkaWVudFVuaXRzPSJ1c2VyU3BhY2VPblVzZSIgeDE9IjAlIiB5MT0iMCUiIHgyPSIwJSIgeTI9IjEwMCUiPgogICAgPHN0b3Agb2Zmc2V0PSIwJSIgc3RvcC1jb2xvcj0iIzhmYzgwMCIgc3RvcC1vcGFjaXR5PSIxIi8+CiAgICA8c3RvcCBvZmZzZXQ9IjEwMCUiIHN0b3AtY29sb3I9IiM2NjhlMDAiIHN0b3Atb3BhY2l0eT0iMSIvPgogIDwvbGluZWFyR3JhZGllbnQ+CiAgPHJlY3QgeD0iMCIgeT0iMCIgd2lkdGg9IjEiIGhlaWdodD0iMSIgZmlsbD0idXJsKCNncmFkLXVjZ2ctZ2VuZXJhdGVkKSIgLz4KPC9zdmc+);
background: -moz-linear-gradient(top, rgba(143,200,0,1) 0%, rgba(102,142,0,1) 100%);
background: -webkit-gradient(linear, left top, left bottom, color-stop(0%, rgba(143,200,0,1)), color-stop(100%, rgba(102,142,0,1)));
background: -webkit-linear-gradient(top, rgba(143,200,0,1) 0%, rgba(102,142,0,1) 100%);
background: -o-linear-gradient(top, rgba(143,200,0,1) 0%, rgba(102,142,0,1) 100%);
background: -ms-linear-gradient(top, rgba(143,200,0,1) 0%, rgba(102,142,0,1) 100%);
background: linear-gradient(top, rgba(143,200,0,1) 0%, rgba(102,142,0,1) 100%);
filter: progid:DXImageTransform.Microsoft.gradient( startColorstr='#8fc800', endColorstr='#668e00', GradientType=0 );
-webkit-box-shadow: 0px 0px 7px rgba(0,0,0,0.2), 0px 0px 0px 1px rgba(188,188,188,0.1);
-moz-box-shadow: 0px 0px 7px rgba(0,0,0,0.2), 0px 0px 0px 1px rgba(188,188,188,0.1);
box-shadow: 0px 0px 7px rgba(0,0,0,0.2), 0px 0px 0px 1px rgba(188,188,188,0.1);
-webkit-transition: box-shadow 0.3s ease-in-out;
-moz-transition: box-shadow 0.3s ease-in-out;
-o-transition: box-shadow 0.3s ease-in-out;
transition: box-shadow 0.3s ease-in-out;
}
and change the "Background" rule. We have used Gradient Color to generate the background color. You can create your own from this address below: