I am brand new to your templates, maybe there is a trivial solution to this problem which I have overlooked. Some buttons look like they should (and like on your Perfect Demo), others show only the background color. The text of the button becomes visible after a mouse over. Could you please guide me where to go to fix this? Happens, for example, when I log in to the frontend with edit rights, so the category listing has a "New" button at the bottom to add additional article - but it is just dark blue. Or when, in the frontend, I click on the Create Article in the Menu (=Menu Item Type). The form has three buttons (Save, Cancel and Switch Editor), but one of them (Save) is just a dark blue box. See the uploaded images of both.

Hi there,
its the bootstrap.css issue and please override the button color with your own custom.css
Add this code below to your css/custom.css

.btn-primary, .btn-info, .btn-inverse {
color: #fff;
}

Thank you very much, the code provided by you fixed it.