Adjust button colors, spinner and check for auth on every page refresh

Created by: artemruts

Description

Closes #21546 (closed) (https://sourcegraph.atlassian.net/browse/COREAPP-30)

Notes

I didn't resize the spinner buttons because it's a standard behavior and should be addressed my a component library, instead will display [spinner + text]. This way buttons that have spinners will be consistent with modal popup-ups on the same page.