Optimizing the new login screen for light themes

[dartcafe]

Comming from #6303

Expected behaviour

Darken elements on the page

Actual behaviour

Some elements are not visible (texts, icons, etc.)

Server configuration

Nextcloud version: 13.0.0 alpha Build:2017-08-29T22:01:17+00:00

Updated from an older Nextcloud/ownCloud or fresh install: fresh install

The new login screen ist great, but maybe some enhancement is to be done, if a light theme is choosen. See examples below.

See examples:

A suggestion (didn't get the background image to invert):

Or maybe the input fields should just get a border instead of darkening them.

[juliusknorr]

Fix for that is also in #6082 Please help reviewing.

[juliusknorr]

Fixes with #6082