The matter is that no Outlook desktop version supports the background images because of background-image style applied for pics displaying in stripe or container: this style is not supported by this email client.
To add the Outlook-friendly background image, go to Appearance - General settings tab and enable the corresponding function.
In this case, a hidden comment is applied in the program code, and it only works with Outlook and it allows users to see a background image.
Also you can add a background color to container, structure and stripe in the editor.
It will be visible in Outlook after the export and in the other ESP, there will be a background image.
You can add a background color to container:
To structure:
And background colours to stripe and content:
If you have any questions, please email us at support@stripo.email.