[adamwathan]

We use it in Tailwind CSS v4 for pill-shaped borders:

  .rounded-full {
    border-radius: calc(1px * infinity);
  }

...as opposed to what everyone has done historically, which is pick some arbitrary huge value like:

  .rounded-full {
    border-radius: 9999px;
  }

No real practical benefit, just satisfyingly more "correct".

[nedt]

Normally 50% is used as each corner is a quarter of the box. Any reason for not simply using that?