Fix sticky diff stats container (#12002)

* Fix sticky diff stats container

* Use pure CSS sticky instead of Fomantic's JS

* add border color to arc-green

* add slight padding on sides

* make linter happy

Co-authored-by: techknowlogick <techknowlogick@gitea.io>

semantic.json

@@ -52,7 +52,6 @@
     "segment",
     "sidebar",
     "site",
-    "sticky",
     "tab",
     "table",
     "text",