Widely available
This feature is well established and works across many devices and browser versions.
Chrome
Edge
Firefox
Safari
fs:xsfont-size: 0.75rem;fs:smfont-size: 0.875rem;fs:mdfont-size: 1rem;fs:lgfont-size: 1.125rem;fs:xlfont-size: 1.25rem;fs:xxlfont-size: 1.5rem;fs:3xlfont-size: 1.875rem;fs:4xlfont-size: 2.25rem;fs:5xlfont-size: 3rem;fs:6xlfont-size: 3.75rem;fs:7xlfont-size: 4.5rem;fs:8xlfont-size: 6rem;fs:9xlfont-size: 8rem;Media Queries
Prefix a class with a breakpoint to apply it from that width up.
Pseudo Classes
Prefix a class with a state to apply it only while that state matches.