Conditional CSS | CSS: Presentation Layer
Standards Based Development
css for conditional processing of parts of style sheets. @supports and @document at-rules are for conditional processing, addressing author and user requirements.
Conditional Group Rules
conditional group rules associate a condition with a group of other css rules; these different rules allow testing different types of conditions, but also share common behavior for how their contents are used when the condition is true and when the condition is false.
Each conditional group rule has a condition, which always evaluates to true or false. When true, css processors must apply the rules inside the group rule as though they were at the group rule's location. When false, css processors must not apply any of the rules inside the group rule. The condition's current state does not affect the css object model, in which the contents of the group rule always remain within the group rule.
Note: this means that when multiple conditional group rules are nested, a rule inside of both of them applies only when all of the rules' condtions are true.