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This still needs a lot of cleanup, but wanted to put what I had up here for your perusal while I'm gone.
But if this is something we still need to do (hiding only when JS is available), couldn't we still use `.no-js`?

```
.menu {
    & {
        display: none; // start off collapsed
    }
    .no-js & {
        display: block !important; // always show when js isn't available
    }
}
```