Nested `<kbd>` should have specific styles

Created by: zlatanvasovic

After reading v3.2.0 changelog, I saw nested <kbd> support has been added.

Problem happens when you want to differ nested and normal <kbd>.

I can't differ should I press Ctrl + , or on special button Ctrl + ,.

My suggestion is to add some specific styling for nested <kbd>s, e.g. font-weight: bold.