There are two sections on the toolbar: a text widget and Thim: Login Popup
To edit those widgets, you can go to your Dashboard => Appearance => Widget => Toolbar, then edit those widgets.
This is our default Text widget on the toolbar:
To change the background of the toolbar, you need to go to your Dashboard => Appearance => Customize => Header => Toolbar, then change the background color.
To change the font and size of the texts on the toolbar, you need to go to your Dashboard => Appearance => Customize => General => Typography, then change the font and font size of the whole website.
If you don’t see the Register option on your Login Popup. The reason is you didn’t enable the register option on your website.
To enable it, you need to go to your Dashboard => Settings => General => General Settings => Membership => enable it.