Though I have tried to modify \"font.size\" in classes like \"Label_control\" and \"sidebar_control\" in the Package \"Theme-Default\", the font size of the editor does not
If you are using the default theme. Just goto Preferences-> Default File Preferences
A new tab pops up.
At about line number you could see the font [font-name] [font-size]
Edit the font-size according to your wish and save.