Comment box tweaks and SVG dropdown triangles (#13376)

* Comment box tweaks and SVG dropdown triangles

- Change all dropdown triangles to SVG
- Bring inline review comment box closer to regular comment boxes
- Enhance arc-green checkbox contrast
- Minor reaction tweaks
- Flexbox the diff file header

* remove a border

* fix type marker in arc-green

* add small code padding

* fix position regression and remove useless rules

Co-authored-by: Lauris BH <lauris@nix.lv>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>

templates/repo/projects/list.tmpl

@@ -28,7 +28,7 @@
 			<div class="ui dropdown type jump item">
 				<span class="text">
 					{{.i18n.Tr "repo.issues.filter_sort"}}
-					<i class="dropdown icon"></i>
+					{{svg "octicon-triangle-down" 14 "dropdown icon"}}
 				</span>
 				<div class="menu">
 					<a class="{{if eq .SortType "oldest"}}active{{end}} item" href="{{$.Link}}?q={{$.Keyword}}&sort=oldest&state={{$.State}}">{{.i18n.Tr "repo.issues.filter_sort.oldest"}}</a>