In case you’re restricted to Font Awesome icons, here are some options of icons to evoke “filling”, which I think would work:
Then, if you must, give these a distinctive color, and/or enclose in a box (with rounded corners, natch!) to make a button.
In case you’re restricted to Font Awesome icons, here are some options of icons to evoke “filling”, which I think would work:
Then, if you must, give these a distinctive color, and/or enclose in a box (with rounded corners, natch!) to make a button.