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/settings/webhook/gitea.tmpl

@@ -11,7 +11,7 @@
 			<div class="ui selection dropdown">
 				<input type="hidden" id="http_method" name="http_method" value="{{if .Webhook.HTTPMethod}}{{.Webhook.HTTPMethod}}{{else}}POST{{end}}">
 				<div class="default text"></div>
-				<i class="dropdown icon"></i>
+				{{svg "octicon-triangle-down" 14 "dropdown icon"}}
 				<div class="menu">
 					<div class="item" data-value="POST">POST</div>
 					<div class="item" data-value="GET">GET</div>
@@ -23,7 +23,7 @@
 			<div class="ui selection dropdown">
 				<input type="hidden" id="content_type" name="content_type" value="{{if .Webhook.ContentType}}{{.Webhook.ContentType}}{{else}}1{{end}}">
 				<div class="default text"></div>
-				<i class="dropdown icon"></i>
+				{{svg "octicon-triangle-down" 14 "dropdown icon"}}
 				<div class="menu">
 					<div class="item" data-value="1">application/json</div>
 					<div class="item" data-value="2">application/x-www-form-urlencoded</div>