Cannot create a toggle switch with React JSS (react-jss) [duplicate] - reactjs

Question

I have seen in a lot of the MUI code that they use pseudo selectors in their react styled components. I thought I would try to do it myself and I cannot get it to work. I'm not sure what I am doing wrong or if this is even possible.
I am trying to make some CSS that will offset this element against the fixed header.
import React from 'react';
import { createStyles, WithStyles, withStyles, Typography } from '#material-ui/core';
import { TypographyProps } from '#material-ui/core/Typography';
import GithubSlugger from 'github-slugger';
import Link from './link';
const styles = () =>
createStyles({
h: {
'&::before': {
content: 'some content',
display: 'block',
height: 60,
marginTop: -60
}
}
});
interface Props extends WithStyles<typeof styles>, TypographyProps {
children: string;
}
const AutolinkHeader = ({ classes, children, variant }: Props) => {
// I have to call new slugger here otherwise on a re-render it will append a 1
const slug = new GithubSlugger().slug(children);
return (
<Link to={`#${slug}`}>
<Typography classes={{ root: classes.h }} id={slug} variant={variant} children={children} />
</Link>
);
};
export default withStyles(styles)(AutolinkHeader);

Answer 1

I found out that the content attribute needed to be double quoted like this
const styles = () =>
createStyles({
h: {
'&::before': {
content: '"some content"',
display: 'block',
height: 60,
marginTop: -60
}
}
});
and then everything worked like expected

Answer 2

As #Eran Goldin said, check the value of your content property and make sure it's set to a string "". Odds are, you are doing something like this:
'&::before': {
content: '',
...
}
Which doesn't set the content property at all in the output stylesheet
.makeStyles-content-154:before {
content: ;
...
}
In Material-UI style object, the content of the string is the css value, including the double quote, to fix it simply write
'&::before': {
content: '""', // "''" will also work.
...
}

Answer 3

Without having to explicitly set a height
The above solutions require explicit height. If you want height to be dynamic, you can do something like this:
&::after {
content: '_'; // Any character can go here
visibility: hidden;
}