Looking at the demo here:
The pager icons for first/last/next/previous are not vertically aligned (See attached picture) for all themes that use round buttons (like "default", blue opal, flat, silver, etc.). However, if you change the style rule for:
.k-pager-wrap > .k-link
and change line-height from 2em to 1.7 or 1.8em, then it's fine.