I want to add “class” in title

You can create a custom template for the content blocks, which allows you add any classes you like. You can use this example for shortcodes and this for widgets.

If you are a less experienced user, adding a class to the containing div will do the trick too (see the FAQ for more info). You can use something like this: [content_block id=198 slug=our-wordpress-plugins class=my-class]

Note that all content blocks have a unique id on the containing div which allows you to use specific styles for them (eg. id="custom_post_widget-5")