refs #17913 [fid_adlr] handle BARF for adlr

* consolidate h1 and h2 headlines and adapt h1 to h2
* increase border on hover by adding inner outline of 2px in sum
* hover / focus: use underline for most links and change color of icons:
** save favorite
** mail
** download
** search history
* change border for hover and focus but keep together mostly, avoid :active settings
* replace dotted lines on hover
* extract buttons and get-It-Box into own files
* improve several format warnings
* add tabindex for main menu
* fix notice for unavailable shard solr4entwickler: set unchecked
* make main menu and main submenu navigable by tab
* emphasize button hover
* handle BARF leading whitespaces in links
* differentiate focus by keyboard and mouse
** example seen in search submit button
** eventually transfer this solution to buttons / dropdowns / selects
* make checkbox mark black
* use custom mixin for border of get-it-boxes
* use azure hover for language menu
* no bold font on hover of buttons
* set focus in lang...