If you want to allow your customers to choose between different text outlines, you will need to create a text outline question.
A text outline question has to be applied on a text.
Creating a text outline question
There are many ways to create a text outline question.
From the text toolbar
Within the text toolbar, click on the A icon, then click on + Outline question.
From the text question
Open your text question.
At the bottom of the right panel, click on + Outline question.
From the add new question menu
Click on the + button in the top left part of the screen.
Under Select input type, you can select Thumbnail, Dropdown or Radio or Label.
Under Select a display type, pick Text outline, then hit Create.
At the bottom of the right panel, under Display type, next to Apply on, click on + Text question and create a new text question or select an existing text question. Your outline will be applied on this text.
Adding outline answers
Once your text outline question is created, you can add outline answers.
Open your text outline question. Within the right side panel, next to Outline answers, hit the + button.
From there, you can set an outline width for each view, pick a color and hit Create.
Clicking on one of the outlines in the customizer's question panel applies it on your text.