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Firefox has this very neat feature called (confusingly enough) userChrome.css which enables users to customize the browser's UI itself through a CSS file. I am using it mainly to have a one-line UI in my browser (like described in this guide) with a unified address and tab bar. I would like to have the same or a similar feature on Chromium-based browsers.
How can I achieve this?
Chromium (and Chrome) do not allow customization of browser components
(user interface) by means of CSS. They do not have the equivalent of userChrome.css.
There exists a file Custom.css with similar function to
userContent.css in Firefox, by means of which you can only alter
the appearance of web pages, not the UI.
Very restricted changes to the browser UI can be achieved by changing themes. It's possible to change colors, but not to move elements or change their size.
A very similar request was done in 2014 at Issue 347016: Support user stylesheets. (It's only one of many such requests.)
The final answer by the developer is quite funny:
This design choice was made by accounting and legal, not by development. Cannot simultaneously fix and keep job. Therefore, won't fix.
The problem is probably that a mechanism for changing the UI could be used as a vector of attack on the user by malware, costly for Google, so the accountants and lawyers won't allow it.
