Change the default font
gedit will use the system fixed-width font by default, but you can change the default gedit font to suit your preferences.
To change the default font in gedit:
Press the menu button in the top-right corner of the window and select Preferences ▸ Font & Colors.
Uncheck the box next to the phrase, "Use the system fixed width font."
Click on the current font name. gedit will open a font-chooser window, allowing you to see available fonts and choose the one that you prefer.
After you have chosen a new font, use the slider under the list of fonts to set the default font size.
Click Select, and then close the dialog.