Change styling for only the Upload File button and Upload/Select Files button

Describe the issue or problem
Hi,
I’m trying change the styling on Upload File button and Upload/Select Files button.

Steps I took leading up to the issue
I used the Web Developer tool in Chrome to isolate the style relating to the buttons
Made the modifications in a CSS file
I uploaded the CSS file to the website
But there is no change

I tried various combinations of classes, but I think I may have missed something or identified the incorrect style?
.pkp_linkaction_addFile
.pkp_linkaction_selectFiles

What application are you using?
OJS 3.3.0.11

Thanks in advance!