Access Button Primary Color In React

I am trying to provide overrides in the theme for buttons that are contained, primary and hovered. I tried this but it doesn't work

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theme/overrides/MuiButton.js

import palette from '../palette';

export default {
  contained: {
    backgroundColor: '#FFFFFF',
    '&.primary': {
      '&:hover': {
        backgroundColor: palette.primary.dark,
      },
    },
  },
};

theme/overrides/index.js

import MuiButton from "./MuiButton";

export default {
  MuiButton
};

theme/index.js

import { createMuiTheme } from "@material-ui/core";

import palette from "./palette";
import typography from "./typography";
import overrides from "./overrides";

const theme = createMuiTheme({
  palette,
  typography,
  overrides,
  zIndex: {
    appBar: 1200,
    drawer: 1100
  }
});

export default theme;

The best resource for determining how to appropriately override the default styles in your theme, is to look at how the default styles are defined.

From https://github.com/mui-org/material-ui/blob/v4.11.0/packages/material-ui/src/Button/Button.js#L138:

  containedPrimary: {
    color: theme.palette.primary.contrastText,
    backgroundColor: theme.palette.primary.main,
    '&:hover': {
      backgroundColor: theme.palette.primary.dark,
      // Reset on touch devices, it doesn't add specificity
      '@media (hover: none)': {
        backgroundColor: theme.palette.primary.main,
      },
    },
  },

Translating this approach to the code in your question would look like this:

import palette from '../palette';

export default {
  containedPrimary: {
    backgroundColor: '#FFFFFF',
    '&:hover': {
      backgroundColor: palette.primary.dark,
    },
  },
};