This extension is free / Pay What you Want on DMsGuild. It is 5e specific and compatible with Unity and Classic.

This extension adds a few extra buttons to the desktop modifier buttons and moves the dice starting position.
The buttons added are the ones defined on the Modifiers window.
Opportunity, Cover, Sup. Cover

Critical, Max, Half

There are two versions of the extension, A and B. The difference is in the layout as seen below.