Button and color enhancements (#24989)

- Various corrections to button styles, especially secondary
- Remove focus highlight, it's annoying when it stays on button after
press
- Clearly define ghost and link buttons with demos in devtest
- Remove black, grey and tertiary buttons, they should not be used
- Make `arc-green` slightly darker

<img width="1226" alt="image"
src="8d89786a-01ab-40f8-ae5a-e17f40e35084">
<img width="1249" alt="image"
src="83651e6d-3c27-46ff-b8bd-ff344d70e949">

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Giteabot <teabot@gitea.io>

web_src/css/repo/list-header.css

@@ -28,9 +28,19 @@
 
 .small-menu-items {
   min-height: 35.4px !important; /* match .small.button in height */
+  background: none !important; /* fomantic sets a color here which does not play well with active transparent color on the item, so unset and set the colors on the item */
 }
 
 .small-menu-items .item {
+  background: var(--color-menu) !important;
   padding-top: 6px !important;
   padding-bottom: 6px !important;
 }
+
+.small-menu-items .item:hover {
+  background: var(--color-hover) !important;
+}
+
+.small-menu-items .item.active {
+  background: var(--color-active) !important;
+}