They are identical display: none keeps its space display: none removes the element from the layout; visibility: hidden hides it but keeps its space visibility: hidden removes it from the layout
The maximum value is 100 z-index applies only to positioned elements (and flex or grid items); a static element ignores it z-index works only on images It needs !important
justify-content controls the vertical alignment Both control the vertical alignment justify-content controls the horizontal (main axis) alignment; align-items controls the vertical (cross axis) alignment Both control the horizontal alignment
It creates columns 1px and 2px wide It creates two columns, with the second taking twice the free space of the first It creates 3 equal columns It is invalid
