I set a background video on the page, but found that there is a wide range of white borders at the bottom of the mobile version. I tried to change the size of different pixels. The results are the same, but everything is normal on the computer version.
Going on the assumption you are using the video as a full-page background, the issue is between how Sparkle’s canvas displays the video versus how web browsers display the video. Sparkle displays in canvas the aspect ratio of the video as is. Browsers adjust the aspect ratio to fit the currently displayed browser window. So while the video’s aspect ratio stays the same in Sparkle’s canvas, your desktop browser will display the background video differently than the mobile version.
Unfortunately, Sparkle doesn’t allow different background video per device, which could allow for different aspect ratios.