On Hello Bar, you can easily customize the design of the text on your pop-ups, all right within the builder itself.

In order to edit the formatting of the text on your pop-up, you will first want to enter into the pop-up builder by either creating a new pop-up or editing an existing pop-up. 

Once you have entered into the builder and gone to the Design tab of the builder, you will be able to click on the text within the pop-up. When you click directly on the text, an Inline Text Editor will appear.

Within the Inline Text Editor, yo will have total control over the styling of your text. 

To see more of the details of how to use the Inline Text Editor, check out this article.