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/user/dashboard/navbar.tmpl

@@ -11,7 +11,7 @@
 							{{if .ContextUser.Visibility.IsPrivate}}<div class="ui red tiny horizontal label">{{.i18n.Tr "org.settings.visibility.private_shortname"}}</div>{{end}}
 						</span>
 					{{end}}
-					<i class="dropdown icon"></i>
+					{{svg "octicon-triangle-down" 14 "dropdown icon"}}
 				</span>
 				<div class="context user overflow menu" tabindex="-1">
 					<div class="ui header">