A banner is essentially a Tour step that displays full width at the top of a page. You can include the same components within a banner as in any other step.
To create this, adjust your step accordingly:
Select Focus > Position > Relative to Screen
Click on the step and then add 100% to the width input
Click on any buttons in the step and choose 'Position = Center right' (this will make the buttons inline with your text)
You can configure any other components as normal. Some suggestions include:
Reduce the corner radius (found by clicking the step) to 0 px
Note: This step will show as part of a Tour. If you'd like to create an independent banner, do not add any other steps to the Tour.