Markdown and Repo header tweaks (#13744)

* Markdown and Repo header tweaks

- Use CSS vars for all markdown colors
- Tweak repo header, removing double borders and adjust sizes
- Use menu instead of buttons for issue open/close switcher
- Add emoji inversion for select emoji glyphs in arc-green
- Use border over box-shadow for all buttons
- Add spacing element to login form without openid

* repo settings navbar fix

* use shared template in more places and adjust dashboard

* fix remaining open/close combos

web_src/less/_repository.less

@@ -225,13 +225,19 @@
 
     .clone.button {
       font-size: 13px;
-      padding: 0 5px;
+      padding: 7.5px 5px;
 
       &:first-child {
         border-radius: var(--border-radius) 0 0 var(--border-radius);
       }
     }
 
+    #repo-clone-https,
+    #repo-clone-ssh,
+    #clipboard-btn {
+      border-right: none;
+    }
+
     .icon.button {
       padding: 0 10px;
     }
@@ -280,6 +286,10 @@
           width: 100%;
         }
       }
+
+      .button + .button {
+        border-left: none;
+      }
     }
 
     #repo-files-table {