You have a couple of settings for styling your form in Airstrip. All of these can be found in the menu on the left in the form editor, when clicking on Form details:
Here are the different options you have and how to use them:
Setting button labels
You can set the text shown in the buttons for two types:
Buttons for going to a next section ("Go to next section")
Buttons for submitting the form ("Submit button label")
You can also add a hint shown underneath the Submit button ("Submit button hint").
Setting a background image
You can set a background image + overlay for your form page, which will be shown on the Thank You page as well. Just click on "Image" for the "Header background style" and you'll see the options pop up:
Adding a progress indicator
If you have several sections and want to show visitors how far they are in completing the form, you can choose to display a progress indicator. This will show the visitor in terms of percentage how many pages are still left.
Note: You can only choose to display a progress indicator when you have 3 page sections or more!