How to remove a style rule of CssCompoer?

Unfortunately, GrapesJS does not have any built-in function like CssComposer.removeRule.

However, you could do that with a workaround like this:

• Get all rules by using CssComposer.getAll(), it will return you a Backbone Collection of all rules.
• I assume that you have the rule model which should be removed, you can use method remove of Backbone Collection to remove it.

const ruleModel = /* the model of rule which you want to remove */;
const allRules = editor.CssComposer.getAll();
allRules.remove(ruleModel);

• If you don't already have rule model, you first need to get the model of selector. Then, you could use method filter of Backbone Collection to find the rules. Finally, remove it `.

function removeRule(willBeRemoveSelector) {
  const willBeRemoveSelectorModel = editor.SelectorManager.get(willBeRemoveSelector);
  const allRules = editor.CssComposer.getAll();
  const willBeRemoveRules = allRules.filter(rule =>
    return rule.get('selectors').has(willBeRemoveSelectorModel)
  });
  allRules.remove(willBeRemoveRules);
}

removeRule('.some-class')

@longdoan7421 is correct but in the second solution I'd use CssComposer.getRule directly

  const willBeRemoveRules = editor.CssComposer.getRule(willBeRemoveSelector);