Hi there,
If you wish to change the length of your read more button I may suggest you to change the line-height of your button as for example you want to make it to 25px so you may add this code into your CSS:
.post-more {
position: absolute;
bottom: 20px;
left: 8%;
text-shadow: 0 1px 2px #111!important;
padding: 0px 15px;
cursor: pointer;
-webkit-border-radius: 3px;
-moz-border-radius: 3px;
-border-radius: 3px;
border-radius: 3px;
border-width: 1px;
border-style: solid;
-webkit-box-shadow: 0 1px 0 rgba(255, 255, 255, 0.3) inset, 0 1px 2px rgba(0, 0, 0, 0.29);
-moz-box-shadow: 0 1px 0 rgba(255, 255, 255, 0.3) inset, 0 1px 2px rgba(0, 0, 0, 0.29);
-box-shadow: 0 1px 0 rgba(255, 255, 255, 0.3) inset, 0 1px 2px rgba(0, 0, 0, 0.29);
box-shadow: 0 1px 0 rgba(255, 255, 255, 0.3) inset, 0 1px 2px rgba(0, 0, 0, 0.29);
color: #fff;
text-shadow: 0 1px 0px #000;
font-size: 13px;
line-height: 25px;
text-align: center;
}
Hope this helps!
Thanks.