Fix the appearance of select boxes in VitePress/Altair embeddings

[WillHannon-MCB]

The select box wasn't visible in Altair plots embedded in VitePress. VitePress removes the browser-determined styling of select boxes so developers can design a custom appearance.

select {
    -webkit-appearance: none;
}

Explicitly specifying the select box's appearance is reasonable in a complex website, but the browser defaults are fine for us, so I overwrote the VitePress styles.

select {
    -webkit-appearance: auto;
}

[WillHannon-MCB]

@jbloom, we also need to modify the styles in Bernadeta's repo to fix this issue.

I'll fix the issue if you give me permissions for that repo.

[Bernadetadad]

@WillHannon-MCB I gave you access