Search and Diff CSS enhancements (#14050)

* Search and Diff CSS enhancements

- Use flexbox for language stats
- Improve labels and code boxes on repo and code search
- Use flexbox on diff header and improve suppressed diff text
- Add dedicated color for diff expander

* more diff tweaks, less vertical padding on header

* more minor tweaks

* always show fold icon, image diff improvments

* remove margin

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>

web_src/less/_review.less

@@ -122,19 +122,14 @@
   color: var(--color-text);
 }
 
-a.fold-file {
-  margin-right: 10px;
-  color: inherit;
-}
-
 a.blob-excerpt {
-  color: #575a68;
+  color: var(--color-text-light);
   height: 28px;
   display: flex;
   justify-content: center;
   align-items: center;
   width: 100%;
-  background: var(--color-primary-light-5);
+  background: var(--color-expand-button);
 }
 
 a.blob-excerpt:hover {