What am I missing? `closest [[CSS selector]]`

[SHxKM]

_="on htmx:afterRequest remove .hidden from the closest <.followbutton/> to me"

Is giving me a "returned null" error.

Snippet from HTML:

<button _="on htmx:afterRequest remove .hidden from the closest <.followbutton/> to me"></button>
<button class="hidden"></button>

document.querySelector('.followbutton')

Does return results.

What am I missing about how closest or CSS literals work?