PX, REM and EM: Choosing CSS Units That Scale
Understand the difference between fixed and relative CSS units before converting design values.
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Pixels are direct; relative units depend on context
A pixel value is explicit. Rem is calculated from the root font size, while em is calculated from the current element or inherited context.
Relative units can improve scaling, but only when the project uses a clear and consistent base.
Use conversion as a starting point
At a 16px root size, 24px equals 1.5rem. That mathematical result does not automatically mean every 24px value should be converted.
Test typography, spacing and component dimensions at normal and enlarged browser text settings.