setting html {overflow: hidden} on mobile cannot hide the scroll bar. What is the principle? 
 there is also a scroll bar that floats and does not take up space. What"s the difference other than that? 
 added: 
 what I said about hiding invalid has been encountered before, and the CSS World P.167 of Zhang Xinxu"s predecessor also mentioned this point: 
on the PC side, set the overflow: hidden hidden scroll bar on the < html > tag to disable scrolling, but it is basically invalid on the mobile side.
