Blockmanager: adding custom class gjs-block-category / gjs-title DIVs

I have a list of categories, and I want to mark some with a different style depending on if they are required or not.

 <div class="gjs-block-categories">
  <div class="gjs-block-category gjs-open" style="order: 1;">
    <div class="gjs-title">
      <i class="gjs-caret-icon fa fa-caret-down"></i>
      Logo
    </div>
    <div class="gjs-blocks-c" style="">

so ideally i could add a class to the div with class 'gjs-title' so that it says 'gjs-title required-field'

this.editor.BlockManager.getCategories(); returns an array of all my block-categories, but my question is how do I go about selecting one in order to use .addClass() ?

if I go by the 'id', and I put

this.editor.BlockManager.get('logos').addClass('required-field')

this doesnt seem to work. What is the best way to select the gis-block-category DIVs to be able to .addClass() or is there a better approach, thanks!