CSS conditional rules
The CSS conditional rules module lets you define a set of rules that will only apply based on the capabilities of the processor or the document the style sheet is being applied to.
Reference
At-rules
Specifications
Browser compatibility
css.at-rules.import
BCD tables only load in the browser
css.at-rules.media
BCD tables only load in the browser
css.at-rules.supports
BCD tables only load in the browser
css.at-rules.document
BCD tables only load in the browser