On many places, it is written, just add this code to CSS.
Then I tried that code/functionality to Admin Settings> Customize> Themes> Edit CSS/HTML. And paste the given code under ‘CSS’ or last pane ‘Embedded CSS’.
But there is no result.
Is there any guide which could tell the basics of how css/html code is pasted and in which area (there are many other panes/tabs also: ; Header ; After Header ; ; Footer )