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Can't get 'selected' or 'hover colors to work for ListItem. For selected tried setting its classes like:

<ListItem selected button key="home" classes={{ selected: classes.listItemSelected }}>
  <ListItemText primary="Hi"/>
</ListItem>

and then setting the style like:

const useStyles = makeStyles((theme) => ({
  listItemSelected:{
    backgroundColor: "#ff0000",
  },
}));

But it doesn't do anything, the 'selected' is described in the ListItem component API here.

How do you get to set the color of both the selected and hover for ListItem?

Answers

Below is the portion of the default ListItem styles that deals with the background color:

export const styles = (theme) => ({
  /* Styles applied to the (normally root) `component` element. May be wrapped by a `container`. */
  root: {
    '&$focusVisible': {
      backgroundColor: theme.palette.action.selected,
    },
    '&$selected, &$selected:hover': {
      backgroundColor: theme.palette.action.selected,
    },
    '&$disabled': {
      opacity: 0.5,
    },
  },
  /* Pseudo-class applied to the `component`'s `focusVisibleClassName` prop if `button={true}`. */
  focusVisible: {},
  /* Styles applied to the inner `component` element if `button={true}`. */
  button: {
    transition: theme.transitions.create('background-color', {
      duration: theme.transitions.duration.shortest,
    }),
    '&:hover': {
      textDecoration: 'none',
      backgroundColor: theme.palette.action.hover,
      // Reset on touch devices, it doesn't add specificity
      '@media (hover: none)': {
        backgroundColor: 'transparent',
      },
    },
  },
  /* Pseudo-class applied to the root element if `selected={true}`. */
  selected: {},
});

The important thing to notice is that the selected styling is done via a combination of two classes (root and selected), so if you try to override it using a single class you will not have sufficient specificity.

Below is an example showing one way to override the selected and hover states:

import React from "react";
import { makeStyles, withStyles } from "@material-ui/core/styles";
import List from "@material-ui/core/List";
import MuiListItem from "@material-ui/core/ListItem";
import ListItemIcon from "@material-ui/core/ListItemIcon";
import ListItemText from "@material-ui/core/ListItemText";
import Divider from "@material-ui/core/Divider";
import InboxIcon from "@material-ui/icons/Inbox";
import DraftsIcon from "@material-ui/icons/Drafts";

const useStyles = makeStyles((theme) => ({
  root: {
    width: "100%",
    maxWidth: 360,
    backgroundColor: theme.palette.background.paper
  }
}));

const ListItem = withStyles({
  root: {
    "&$selected": {
      backgroundColor: "red",
      color: "white",
      "& .MuiListItemIcon-root": {
        color: "white"
      }
    },
    "&$selected:hover": {
      backgroundColor: "purple",
      color: "white",
      "& .MuiListItemIcon-root": {
        color: "white"
      }
    },
    "&:hover": {
      backgroundColor: "blue",
      color: "white",
      "& .MuiListItemIcon-root": {
        color: "white"
      }
    }
  },
  selected: {}
})(MuiListItem);

export default function SelectedListItem() {
  const classes = useStyles();
  const [selectedIndex, setSelectedIndex] = React.useState(1);

  const handleListItemClick = (event, index) => {
    setSelectedIndex(index);
  };

  return (
    <div className={classes.root}>
      <List component="nav" aria-label="main mailbox folders">
        <ListItem
          button
          selected={selectedIndex === 0}
          onClick={(event) => handleListItemClick(event, 0)}
        >
          <ListItemIcon>
            <InboxIcon />
          </ListItemIcon>
          <ListItemText primary="Inbox" />
        </ListItem>
        <ListItem
          button
          selected={selectedIndex === 1}
          onClick={(event) => handleListItemClick(event, 1)}
        >
          <ListItemIcon>
            <DraftsIcon />
          </ListItemIcon>
          <ListItemText primary="Drafts" />
        </ListItem>
      </List>
      <Divider />
      <List component="nav" aria-label="secondary mailbox folder">
        <ListItem
          button
          selected={selectedIndex === 2}
          onClick={(event) => handleListItemClick(event, 2)}
        >
          <ListItemText primary="Trash" />
        </ListItem>
        <ListItem
          button
          selected={selectedIndex === 3}
          onClick={(event) => handleListItemClick(event, 3)}
        >
          <ListItemText primary="Spam" />
        </ListItem>
      </List>
    </div>
  );
}

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