.awesome{
background: #222 url(/images/alert-overlay.png) repeat-x;
display: inline-block;
padding: 5px 10px 6px;
color: #fff;
text-decoration: none;
font-weight: bold;
line-height: 1;
-moz-border-radius: 5px;
-webkit-border-radius: 5px;
-moz-box-shadow: 0 1px 3px #999;
-webkit-box-shadow: 0 1px 3px #999;
text-shadow: 0 -1px 1px #222;
border-bottom: 1px solid #222;
position: relative;
cursor: pointer;
-moz-box-shadow: 0 1px 3px rgba(0,0,0,0.5);
-webkit-box-shadow: 0 1px 3px rgba(0,0,0,0.5);
text-shadow: 0 -1px 1px rgba(0,0,0,0.25);
border-bottom: 1px solid rgba(0,0,0,0.25);
}


* Sizes ---------- */
.small.awesome {
font-size: 11px;
}
.medium.awesome {
font-size: 13px;
}
.large.awesome {
font-size: 14px;
padding: 8px 14px 9px;
}
 
/* Colors ---------- */
.blue.awesome {
background-color: #2daebf;
}
.red.awesome {
background-color: #e33100;
}
.magenta.awesome {
background-color: #a9014b;
}
.orange.awesome {
background-color: #ff5c00;
}
.yellow.awesome {
background-color: #ffb515;
}

http://www.zurb.com/article/266/super-awesome-buttons-with-css3-and-rgba

Super Awesome Buttons with CSS3 and RGBA

CSS