TYPO3 Core

The patch broke page module drag & drop, see related issue. Reverted for now.

The extra margin is added from the #t3-login-form in /typo3/sysext/t3skin/stylesheets/structure/login_screen.css

I think you can´t combine percentual and auto margins for this div-container.

Just remove the 10% top-margin and add a top-padding of 10% for the #t3-login-form. This should fix the problem without breaking the page module drag & drop

The resulting CSS looks like this:

#typo3-index-php #t3-login-form {
  margin: 0 auto;
  width: 430px;
  padding: 10% 0 0 0;
}

Thank you Torben for investigating this further.
Would you mind pushing your change to Gerrit?

Pushed to Gerrit - https://review.typo3.org/#/c/17067/

Patch set 1 for branch master has been pushed to the review server.
It is available at https://review.typo3.org/17282