HTML
<button href="#" class="back"><span></span>Back</button>
CSS
.button {
color: #fff;
text-decoration: none;
display: inline-block;
padding: 4px 10px;
-webkit-border-radius: 5px;
}
.button.black {
background-image: -webkit-gradient(linear, left top, left bottom,
from(#7d828c),
color-stop(0.5, #303749),
color-stop(0.5, #121a2e),
to(#121a2e));
border: solid 1px rgba(79, 79, 79, 0.75);
}
.button.black:hover {
background-image: -webkit-gradient(linear, left top, left bottom,
from(#4286f5),
color-stop(0.5, #4286f5),
color-stop(0.5, #194fdb),
to(#194fdb));
}
.button.back {
position: relative;
padding-left: 5px;
margin-left: 8px;
}
.button.back > span{
display: block;
height: 20px;
width: 20px;
background-image: -webkit-gradient(linear, left top, right bottom,
from(#7d828c),
color-stop(0.5, #303749),
color-stop(0.5, #121a2e),
to(#121a2e));
border-left: solid 1px rgba(79, 79, 79, 0.75);
border-bottom: solid 1px rgba(79, 79, 79, 0.75);
-webkit-transform: rotate(45deg);
-webkit-mask-image: -webkit-gradient(linear, left bottom, right top,
from(#000000),
color-stop(0.5,#000000),
color-stop(0.5, transparent),
to(transparent));
position: absolute;
left: -10px;
top: 2px;
}
Source: Create Back & Next Buttons with CSS3