Why does AccordionSummary background change to grey when clicking inside TextField in Material-UI?

Question

I am using Material-UI's Accordion and inside AccordionSummary I have a <TextField /> (which is actually controlled by Formik and formik-material-ui) and the background of AccordionSummary turns grey when clicking inside the field only. I don't want it to do this and it doesn't appear to be anything configured by the Accordion API, unless I am missing something. How can I stop it from behaving this way?

I've recreated the issue on Codesandbox.

Here's the full code from the sandbox:

import React from "react";
import { Formik, Field, Form, ErrorMessage } from "formik";
import { TextField, CheckboxWithLabel, Select } from "formik-material-ui";
import Grid from "@material-ui/core/Grid";
import Box from "@material-ui/core/Box";
import FormControl from "@material-ui/core/FormControl";
import MenuItem from "@material-ui/core/MenuItem";
import Button from "@material-ui/core/Button";
import Accordion from "@material-ui/core/Accordion";
import AccordionDetails from "@material-ui/core/AccordionDetails";
import AccordionSummary from "@material-ui/core/AccordionSummary";

export default function App() {
  return (
    <div className="App">
      <Formik>
        <Form>
          <Accordion>
            <AccordionSummary>
              <FormControl fullWidth>
                <Field
                  component={TextField}
                  name="itemName"
                  placeholder="What do you want to buy?"
                  variant="outlined"
                />
              </FormControl>
            </AccordionSummary>
            <AccordionDetails>
              <Grid container>
                <Grid item xs={2}>
                  <Box pt={2}>
                    <FormControl fullWidth>
                      <Field
                        component={TextField}
                        name="quantity"
                        label="Qty"
                        type="number"
                        variant="outlined"
                        size="small"
                      />
                    </FormControl>
                  </Box>
                </Grid>
                <Grid item xs={2}>
                  <Box pt={2} pl={1}>
                    <FormControl fullWidth>
                      <Field
                        component={TextField}
                        name="volume"
                        label="Vol"
                        type="number"
                        variant="outlined"
                        size="small"
                      />
                    </FormControl>
                  </Box>
                </Grid>
                <Grid item xs={2}>
                  <Box pt={2} pl={1}>
                    <FormControl label="Type" size="small" fullWidth>
                      <Field
                        component={Select}
                        name="volumeType"
                        as="select"
                        variant="outlined"
                      >
                        <MenuItem value="g">grams</MenuItem>
                        <MenuItem value="kg">kg</MenuItem>
                        <MenuItem value="ml">ml</MenuItem>
                        <MenuItem value="cl">cl</MenuItem>
                        <MenuItem value="litre">litre</MenuItem>
                        <MenuItem value="pint">pint</MenuItem>
                        <MenuItem value="pack">pack</MenuItem>
                      </Field>
                    </FormControl>
                  </Box>
                </Grid>
                <Grid item xs={4}>
                  <Box pt={2} pl={1}>
                    <FormControl fullWidth>
                      <Field
                        component={TextField}
                        name="brandName"
                        label="Brand"
                        variant="outlined"
                        size="small"
                      />
                    </FormControl>
                  </Box>
                </Grid>
                <Grid item xs={2}>
                  <Box pt={2} pl={1}>
                    <Button
                      type="submit"
                      variant="contained"
                      color="primary"
                      disableElevation
                      fullWidth
                    >
                      Add
                    </Button>
                  </Box>
                </Grid>
              </Grid>
            </AccordionDetails>
          </Accordion>
        </Form>
      </Formik>
    </div>
  );
}

Answer 1

What you are seeing is the focused styling for AccordionSummary. You can observe this in the Accordion demos as well by clicking on an accordion and then using the Tab key to move to the next AccordionSummary. This is there for accessibility reasons so that the user can tell where focus is within the Accordion when navigating with the keyboard.

You can override this with the following:

import MuiAccordionSummary from "@material-ui/core/AccordionSummary";
import { withStyles } from "@material-ui/core/styles";

const AccordionSummary = withStyles({
  root: {
    "&.Mui-focused": {
      backgroundColor: "inherit"
    }
  }
})(MuiAccordionSummary);