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/pull.tmpl

@@ -336,7 +336,7 @@
 									</span>
 								</button>
 								<div class="ui dropdown icon button">
-									<i class="dropdown icon"></i>
+									{{svg "octicon-triangle-down" 14 "dropdown icon"}}
 									<div class="menu">
 										{{if $prUnit.PullRequestsConfig.AllowMerge}}
 										<div class="item{{if eq .MergeStyle "merge"}} active selected{{end}}" data-do="merge">{{$.i18n.Tr "repo.pulls.merge_pull_request"}}</div>

templates/repo/issue/view_content/sidebar.tmpl

@@ -502,7 +502,7 @@
 							<div class="ui fluid action input">
 								<div class="ui search selection dropdown" id="new-dependency-drop-list" data-issue-id="{{.Issue.ID}}">
 									<input name="newDependency" type="hidden">
-									<i class="dropdown icon"></i>
+									{{svg "octicon-triangle-down" 14 "dropdown icon"}}
 									<input type="text" class="search">
 									<div class="default text">{{.i18n.Tr "repo.issues.dependency.add"}}</div>
 								</div>
@@ -571,7 +571,7 @@
 									<option value="{{.}}">{{.}}</option>
 								{{end}}
 							</select>
-							<i class="dropdown icon"></i>
+							{{svg "octicon-triangle-down" 14 "dropdown icon"}}
 
 							<div class="default text"> </div>