no-js tab switcher

Re: https://stackoverflow.com/a/71008554

```css
dialog { display: block; }

dialog:not(:target):not([open]) { display: none; }
```

```html

Open dialog

Dialog

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.

Close

```

Not sure if this would have to enumerate every hash target (ex: `#main`, `#settings`) or if this could be done by some sort of dynamic class selector, but this should allow tabs without JavaScript.

No repository file or test is named; start by reviewing the existing boilerplate structure and the CSS/HTML examples in this issue. Determine how the tab targets should be represented, then verify that tabs can switch and close without JavaScript.

Written by the indexing model from the issue text.