These inputs are somewhat nonsensical, as they don't represent valid CSS syntax. It would be clearer if you just asserted properly formatted input (and then omit the second parameter, because it defaults to the first).

```js
btc("#foo:hover {\n  color: purple\n}\n");
btc("::selection {\n  color: #ff0000;\n}\n");
```

Note that the second test has an added `\n`, which fixes one breaking test. The `#foo:hover` case is still breaking.