Why some classes silently do nothing

The prebuilt stylesheet includes the standard set of classes but NOT the ones generated on the fly: opacity through a slash, arbitrary values in brackets, and half of the colours.

bg-white/80      does not work
text-[13px]      does not work
bg-emerald-500   does not work
bg-indigo-500    works

The class is simply absent from the file, so there is no error — the block just stays unstyled. Before using an unfamiliar class, look for it in the build itself, and write anything non-standard as ordinary CSS.