Looks good to me

I'd highly suggest you make it into a more formal pull request on gerrit.

And potentially post to the mailing lists too

Are you aware of Timeless (T154371)?

Yes I am aware of it.

Screenshot
http://i.imgur.com/xuz0wik.png

Please upload screenshots locally: https://phabricator.wikimedia.org/file/upload/

I fail to see how this is more "minimalistic", since the interface elements are the same. Actually, you add more stuff, i.e. three rectangles in which to divide the interface.

For clarity, should this report be re-titled to "Make Vector clickable elements not have borders or separations"? Note that the tabs' text tends to get quite mixed up in languages where the strings are long and/or in devices where there is less space.

Change 358229 had a related patch set uploaded (by LegoFan4000; owner: Golopotw):
[mediawiki/skins/Vector@master] Make Vector look more minimalistic

https://gerrit.wikimedia.org/r/358229

I don't think this patch can be merged. This is a very large change to the design of the skin. I would recommend that you turn this into a new skin, based on Vector (http://blog.redwerks.org/2012/02/28/mediawiki-subskin-tutorial/). I think users of existing wikis (including Wikimedia wikis', but not only) would be unhappy to see the interface changed suddenly after updating the skin.

Thanks for your advice, I am finding a good way to refactor every "Vector" into a new name, preferably automatically so that changes can be pulled easily.

It's possible that changes can be made to Vector in very small increments, but each one needs to be a separate commit and bug, invite lots of feedback and be thoroughly tested. There is a lot of CSS code in extensions, gadgets and per-wiki CSS configs that make assumptions about how Vector currently looks, so even making small changes to the toolbar or sidebar could result in some very broken behaviour.

Example: T168420