Use the .align-items-*-center classes to align single rows of items in the center of a flex container on different screens.
Resize the browser window to see the effect. Note: align-items-stretch is default.
.align-items-center:
.align-items-center
.align-items-sm-center:
.align-items-sm-center
.align-items-md-center:
.align-items-md-center
.align-items-lg-center:
.align-items-lg-center
.align-items-xl-center:
.align-items-xl-center
.align-items-xxl-center:
.align-items-xxl-center