After I've upgraded to DNN 7, it breaks some of my styles. Take for example the stylesheet Portals/_default/admin.css at line 179.

The z-index for body > form > .RadWindow is set as 3002 !important

Why would anyone style that as !important? I have multiple modal RadWindows which some of them have to be on top of others. This forces all of my RadWindows to have the same z-index and breaks everything. I set the z-index of my RadWindows as inline style. Even if I apply the style at skin level (skin.css), it won't work because default.css has a higher precedence.

And I can't modify those default style sheets since the next version upgrade will overwrite my changes. I can't do it at the module level either because there are too many modules to modify. This is one of the example of the problem that I spotted unwittingly. I'm sure there are more problem related to style. I couldn't be going through all my custom modules page by page to make sure everything is in order. This is exasperating.

Why would the default style be set to !important in the first place anyway? This will render skin styling impossible since styles in skin.css can't override those in default.css.

I am having CSS issues on several projects after upgrading them to 7.

The default styles are very heavy-handed and seem to be spread all over - not just default.css.
So I'm playing a tedious game of discovery, trial and error to try and get things back to good.

I don't understand why the DNN team is silent on these issues and why we aren't getting a bit more information on how to work with the DNN 7 styling model.

It's very frustrating!