SyntaxError for valid CSS

Hello, the following works:

```css
:where([aria-hidden="false" i][hidden]) {
  display: initial;
}
```

While the following does not: 

```css
:where([aria-hidden="false" i][hidden]:not(:focus)) {
  display: initial;
}
```

It gives the following error:

```
SyntaxError: expected ']' got 'i'
```

This is with `lessc 4.1.2 (Less Compiler) [JavaScript]`.

Thank you!