some more 516 compat fixes (#89766)

Ports the helpers from
https://github.com/BeeStation/BeeStation-Hornet/pull/12240

This should fix some more of the 516 issues that I've seen while giving
a quick check through the code

The remaining browse should work now.

Also fixing another sass warning while being on it.

## About The Pull Request
## Why It's Good For The Game
## Changelog
🆑
fix: tgui say 516 will no longer change channels when the button is used
to drag it
fix: tgui say 516 will no longer leak radio messages into the wrong
channel
fix: runechat flickering when faded up messages fade out
/🆑

code/modules/client/client_procs.dm

@@ -441,7 +441,7 @@ GLOBAL_LIST_INIT(blacklisted_builds, list(
 			msg += "Your version: [byond_version].[byond_build]<br>"
 			msg += "Required version to remove this message: [warn_version].[warn_build] or later<br>"
 			msg += "Visit <a href=\"https://secure.byond.com/download\">BYOND's website</a> to get the latest version of BYOND.<br>"
-			src << browse(msg, "window=warning_popup")
+			src << browse(HTML_SKELETON(msg), "window=warning_popup")
 		else
 			to_chat(src, span_danger("<b>Your version of byond may be getting out of date:</b>"))
 			to_chat(src, CONFIG_GET(string/client_warn_message))