replacing arrow images in magnificPopup

Question

I was able to replace the close button in magnificPopup with a custom graphic, but I can't seem to figure out similar code to do the same with the next and previous buttons. Any suggestions?

Here is the code for the close button:

closeMarkup: '<button title="%title%" class="mfp-close" style="position: absolute; top: -50px;"><img src="images/proj_images/tmp.jpg" width="25" height="29"/></button>',