Dear 婷 黄,
Thank you for your question.
If I understand well and based on your other question, in a "Text Document", you would like to replace the default background by your custom background.
Currently, in a "Text Document" part, it is not possible to change the background, as the defaut lines we display are mandatory to have a good accuracy when writing text.
You may nevertheless proceed another way:
-You should be in a "Text" part
-Ensure you disable the guidelines.
-In a custom view, you can add your background image in a view on top of our background.
=>you nevertheless understand you will not have the "Text Document" possibilites, such as adding blocks as only the "Text Document" is a container part.