Specifying `@media` at rules and pseudo selectors `:last-child` together

### Describe the issue

So I have the following styles specified:

```ts
const styles = stylex.create({
container: {
marginBottom: {
default: '0.5rem',
'@media screen and (min-width: 800px)': '0.75rem',
':last-child': 0
}
}
})
```

### Expected behavior

I want my `margin-bottom` to always be `0` when as a last child element, otherwise `0.5rem` and `0.5rem` on larger screens. However `':last-child'` never works on larger screen. I'd like to know the proper way to do so.

### Steps to reproduce

```tsx
import * as stylex from '@stylexjs/stylex';

const styles = stylex.create({
container: {
marginBottom: {
default: '0.5rem',
'@media screen and (min-width: 800px)': '0.75rem',
':last-child': 0
}
}
});

### Test case

_No response_

### Additional comments

_No response_