Comparison
TiervsLayer
Tier
Defined by the difference stated below.
Layer
you put the vendor stylesheet in a lower layer and your one-class rule now beats its id selectors.
Named buckets declared with `@layer` that are compared before specificity, so an entire body of CSS can be placed above or below another regardless of how its selectors are written. It is the intended answer to the third-party override problem that `!important` used to be. The catch is that unlayered styles beat every layer, so partial adoption inverts the result you expected.
Full entry →The difference
A layer is a logical grouping of code; a tier is a physical place it runs. Three layers can live in one process and one deployable, and usually should — the classic three-tier picture put them on separate machines because that was how you scaled in the nineties. Keeping the two words apart is what stops a layering discussion turning into a deployment argument.
Entry: Tier vs layer →