Issues using linear-gradient with CSS

I have two buttons (one outlined and one filled) and I am trying to set various parts of them to be a gradient using linear-gradient but the gradient never displays. If I substitute the linear-gradient() with #000000 the text/border show up as black just fine.

Anyone proficient in CSS able to help me out? I also did try -webkit-linear-gradient to no avail…

This might be a bug. Can you fill an issue on GitHub about this. Please include the template code as well