Replace `:nth-child(n)` with `sibling-count()` in `calc()`

[what1s1ove]

• feat(whatislove-dev): add sticker to background wd-515 #517
• for paw text ?

[what1s1ove]

Depends on https://developer.mozilla.org/en-US/docs/Web/CSS/sibling-index#browser_compatibility