arrow image not showing up in IE8

The plugin works great in all of the browsers I’ve tested except IE8. I found a workaround in this forum for fixing the background hover color using my themes CSS, but right now the “To Top” button appears as a square with no up arrow image. I know the easy solution would be to use “text” rather than the arrow but I like the look of it. Is there a fix for this?

https://www.ads-software.com/extend/plugins/dynamic-to-top/