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/helpers.less

@@ -12,12 +12,16 @@
 .f1 { flex: 1 !important; }
 .fw { flex-wrap: wrap !important; }
 .vm { vertical-align: middle !important; }
+.w-100 { width: 100% !important; }
+.h-100 { height: 100% !important; }
 
 .mono {
   font-family: var(--fonts-monospace) !important;
   font-size: .9em !important; /* compensate for monospace fonts being usually slighty larger */
 }
 
+.bold { font-weight: 600 !important; }
+
 .word-break {
   word-wrap: break-word !important;
   word-break: break-all !important;