Buttons and dropdowns need highlight and icon split

Before the button rework text buttons have been grey.
Now they are red per default.
I guess we should only make them red for the big posting buttons to draw a bit of attention to them and not colour everything.

The second thing is the dropdown icon. It now overlaps the content of the buttons. See attached screenshot.
For testing you can use https://github.com/nickvergessen/phpbb-ext-newspage/tree/develop-ascraeus