Hmm now it’s solved so now I can’t record how. But that’s why I asked https://www.ads-software.com/support/topic/sydney-theme-how-to-remove-white-side-space?replies=6
Because Full Width (in Edit Row -> Row Styles -> Theme -> Row Layout) just make the content full width (no right/left padding) in a row, but the row itself doesn’t fill the full width (my colorful row still have padding refer the edge of my browser). I feel confused because the header and footer are in Full Width, why my rows not? I must add some simple CSS code to meet my need. Hehehe.
(Sorry for my terrible English, I’m not a native speaker)