Refactor SCSS styles in common and about templates

- Removed unused styles and nested selectors from _common.scss to streamline the code.
- Cleaned up the .about section in _about.scss by eliminating redundant styles for headings and paragraphs.
- Improved overall readability and maintainability of the SCSS files.

assets/scss/templates/_service.scss

@@ -109,10 +109,6 @@
   }
 }
 
-h2, h3 {
-  margin-bottom: 10px; /* Passe den Wert nach Bedarf an */
-}
-
 .center-container {
   display: flex;
   flex-direction: column;