I would like to edit the theme rules

[Moin]

If you don’t want to fork the theme, you can make your edits in a new theme component which you add to the theme

@Arkshine

If you don’t want to fork the component, you can create a new Theme component and attach it to your theme.

• Go to Admin → Customize
• Click on Install button
  
• Then attach it to your theme and click on Edit CSS/HTML button