[Chrome Extension]Add Elements to Dynamically Rendered Components

Question

I am creating a chrome extension where it should be injecting some elements to div with class "slds-rich-text-editor__toolbar slds-shrink-none slds-rich-text-editor__toolbar_bottom". But this div will be rendered dynamically on click of some buttons. i do not have access to the web page code. i am currently having an event listener for the user to press Shif+S and then i am adding my element. is there anyway to identify in JS if the element has been added and then inject my element automatically? somoething like how Grammerly browser extension add to all the text area boxes.