Adding this answer because the comments in the accepted answer become too long and not complete. As already explained, hidden-* classes no longer exist in the beta version of Bootstrap 4.
"What exactly is hidden-sm-DOWN?"
It no longer exists in beta, but in previous versions it meant "hidden at low and low levels." A value hidden in xs and sm , but otherwise visible.
If you want to hide an element at certain levels (breakpoints) in Bootstrap 4, use the d-* display classes accordingly. Remember that xs is the default breakpoint (always implied) unless it is overridden by a larger breakpoint. Since xs implied, you no longer use the -xs- infix. For example, it is not d-xs-none , it is just d-none .
https://www.codeply.com/go/bRlHp8MxtJ
hidden-xs-down = d-none d-sm-blockhidden-sm-down = d-none d-md-blockhidden-md-down = d-none d-lg-blockhidden-lg-down = d-none d-xl-blockhidden-xl-down = d-none (same as hidden )hidden-xs-up = d-none (same as hidden )hidden-sm-up = d-sm-nonehidden-md-up = d-md-nonehidden-lg-up = d-lg-nonehidden-xl-up = d-xl-nonehidden-xs (only) = d-none d-sm-block (same as hidden-xs-down )hidden-sm (only) = d-block d-sm-none d-md-blockhidden-md (only) = d-block d-md-none d-lg-blockhidden-lg (only) = d-block d-lg-none d-xl-blockhidden-xl (only) = d-block d-xl-nonevisible-xs (only) = d-block d-sm-nonevisible-sm (only) = d-none d-sm-block d-md-nonevisible-md (only) = d-none d-md-block d-lg-nonevisible-lg (only) = d-none d-lg-block d-xl-nonevisible-xl (only) = d-none d-xl-block
Demo of all hidden / visible classes in beta version of Bootstrap 4
Also note that d-*-block can be replaced with d-*-inline , d-*-flex , etc. depending on the type of display of the item. Learn more about displaying classes in beta
See also:
Bootstrap 4 hidden-X- (down / up) class does not work
Missing visible - ** and hidden - ** in Bootstrap v4
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