Tailwind bg opacity

Question

I was curious about the CSS behind tailwinds bg opacity. I could only find 'opacity' in pure CSS but that affects everything rather than just the background. Could somebody please explain this?

Answer 1

See Here in the tailwind docs. The second number indicates the opacity.

<button class="bg-sky-500/100 ..."></button>
<button class="bg-sky-500/75 ..."></button>
<button class="bg-sky-500/50 ..."></button>