The back image in html css is not displayed_html/css_WEB-ITnose

I would like to ask everyone
I used css to introduce an image into the html as the background of , why is it not displayed?
The picture is a scanned piece of A4 paper, and the path is correct. Just quote another one (full-screen screenshot) in the same folder. It’s strange. Please enlighten me.

Reply to the discussion (solution)

Maybe the image format is incorrect, it must be in rgb format in PS

Maybe the image format is incorrect, it must be in rgb format in PS
1.
General format: png, gif....