**Steps to replicate the issue** (include links if applicable):
* Visit https://en.wikipedia.org/wiki/Special:ChangeContentModel
**What happens?**:
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**What should have happened instead?**:
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**Software version** (skip for WMF-hosted wikis like Wikipedia):
**Other information** (browser name/version, screenshots, etc.):
* It violates the principle of least astonishment and is confusing for Sanitized CSS to be selected as the new content model by default. I suggest adding a blank option, then throwing a form validation error if that remains selected.
* Confusingly, in ooui, when text boxes are editable they are white, and when they are not editable (readonly) they are gray. But when combo boxes are editable they are gray, and when they are not editable (readonly) they are gray. Special:ChangeContentModel uses a mix of readonly and editable, with lots of gray, and gray not corresponding to readonly or editable consistently. Since changing the ooui combo box background color doesn't seem likely to me to get merged, I think this approach helps solve that confusion.
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