[DFG-Viewer] Update LESS/CSS for fulltextsearch sites

[csidirop]

The styling given from the DFG-Viewer extension for search sites is incomplete/missing.

Therefore I'll be adding a default styling.

Current dev-branch: https://github.com/csidirop/dfg-viewer/tree/searchpage-styling

[csidirop]

• Codebasis should be finished: https://github.com/csidirop/dfg-viewer/tree/searchpage-styling
• PR is up: https://github.com/slub/dfg-viewer/pull/232
• Branch is already merged into our 6.x-ocr branch because it is to be expected that the PR will not be addressed by the SLUB (https://github.com/UB-Mannheim/dfg-viewer/commit/6862501677fcfdb3e97486fa75417be455649f23)