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>

web_src/less/_base.less

@@ -310,6 +310,17 @@ code,
   flex-direction: inherit;
 }
 
+.ui.dropdown:not(.labeled) > .dropdown.icon {
+  height: 14px;
+  vertical-align: bottom;
+  margin-bottom: -2px;
+  margin-left: .5rem;
+}
+
+.ui.form .field > .selection.dropdown > .dropdown.icon {
+  height: auto;
+}
+
 .ui {
   &.left:not(.action) {
     float: left;
@@ -1118,6 +1129,10 @@ i.icon.centerlock {
   }
 }
 
+.lines-code {
+  padding-left: 5px;
+}
+
 .lines-code code {
   white-space: pre;
 }