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/issue/view_content.tmpl

@@ -20,8 +20,8 @@
 				</a>
 			{{end}}
 				<div class="content">
-					<div class="ui top attached header">
-						<div class="header-left df ac">
+					<div class="ui top attached header comment-header df ac sb">
+						<div class="comment-header-left df ac">
 							{{if .Issue.OriginalAuthor }}
 								<span class="text black">
 									<i class="fa {{MigrationIcon .Repository.GetOriginalURLHostname}}" aria-hidden="true"></i>
@@ -40,7 +40,7 @@
 								</span>
 							{{end}}
 						</div>
-						<div class="header-right actions df ac">
+						<div class="comment-header-right actions df ac">
 							{{if not $.Repository.IsArchived}}
 								{{if gt .Issue.ShowTag 0}}
 									<div class="ui basic label">