code: public function updateCMSFields(FieldList $fields)
      {
          // Insert Icon Tab:
          
          $fields->insertAfter(
              Tab::create(
                  'Icon',
                  $this->owner->fieldLabel('Icon')
              ),
              'Main'
          );
          
          // Create Icon Fields:
          
          $fields->addFieldsToTab(
              'Root.Icon',
              [
                  FontIconField::create(
                      'FontIcon',
                      $this->owner->fieldLabel('FontIcon')
                  ),
                  ColorField::create(
                      'FontIconColor',
                      $this->owner->fieldLabel('FontIconColor')
                  )
              ]
          );
      }
docs: Updates the CMS fields of the extended object.
  
  @param FieldList $fields List of CMS fields from the extended object.
  
  @return void