For better visibility of numbers, names and initials, you have the option of selecting an outline or a rectangular background in your desired color. To do this, click on the corresponding elements and select “Color & background” in the window on the left. Here you can then select an outline and/or a background. You can also adjust the outline thickness as required. You can also add a background to logos to make them stand out better from the jersey design.
https://www.youtube.com/watch?v=VnA_kY9_Hco&list=PLqlk7yRn567-YboPHfIZDilNfWa7m9DUM&index=7