Try adding the html.ccm-toolbar-visible css style to your theme css file and if necessary add the !important declaration to prevent the concrete/css/cms.css file from over-riding it.
CSS are Cascading Style Sheets and they are read by the browser from top to bottom with the first one it encounters at the top and the last one at the bottom.
The last declaration for any given style element will be the one that the browser will use, unless the declaration has !important appended to it.
So for example, if you have several declarations for a H1 element like these H1 {font-size:12px} and H1 {font-size:14px} and H1 {font-size:16px}, whichever is the last one the browser reads will be the one it will use.
However, if you have for example H1 {font-size:12px!important} then the browser will use this important one (or the last important one it encounters).
So for your theme’s css to take precedence it would have to be read by the browser after the other css files, if it is not the last one to be read by the browser then you could append the !important declaration.