Can't get cssclasses to work

I have a simple CSS snippet to remove the strike through from completed checkboxes:

.no-strike body {
    --checklist-done-decoration: none;
}

And I add the cssclasses property to the top of the page:

---
cssclasses:
 - no-strike
---

But the CSS isn't being applied. If I delete the class from the .CSS file, it works just fine, but I want to apply it only to certain documents and I'm told cssclasses is supposed to be the way to do it.

The issue persists if I reload obsidian from the command pallette, and even if I close and reopen obsidian.

What am I doing wrong?