Q:

MaterialUI for React with Styled-Components

I want to style the Paper of MaterialUI's Dialog
const StyledDialog = styled(Dialog)`
  & .MuiPaper-root {
    width: 600px;
  }
`;

However, this means that all elements nested inside the Dialog that have the MuiPaper-root class (for example, other Papers) will inherit it.
Is there any way of scoping this styling only to the Paper used by the first Dialog?

A:

There are a several ways to approach this. One approach is to use child selectors (as mentioned in Kaca992's answer), but the Paper is not a direct child of the Dialog so to use this approach you need & > .MuiDialog-container > .MuiPaper-root. Another option is to use Dialog's PaperComponent prop and provide it with a styled Paper component. A third option is to leverage the MuiDialog-paper CSS class.
All three approaches are shown in the example below.
import React from "react";
import Button from "@material-ui/core/Button";
import DialogTitle from "@material-ui/core/DialogTitle";
import Dialog from "@material-ui/core/Dialog";
import Paper from "@material-ui/core/Paper";
import styled from "styled-components";

const StyledDialog = styled(Dialog)`
  & > .MuiDialog-container > .MuiPaper-root {
    background-color: purple;
  }
`;
const StyledDialog2 = styled(Dialog)`
  & .MuiDialog-paper {
    background-color: blue;
  }
`;
const StyledPaper = styled(Paper)`
  background-color: green;
`;

export default function SimpleDialogDemo() {
  const [open1, setOpen1] = React.useState(false);
  const [open2, setOpen2] = React.useState(false);
  const [open3, setOpen3] = React.useState(false);

  return (
    <div>
      <Button variant="outlined" color="primary" onClick={() => setOpen1(true)}>
        Open dialog using child selectors
      </Button>
      <Button variant="outlined" color="primary" onClick={() => setOpen3(true)}>
        Open dialog using MuiDialog-paper
      </Button>
      <Button variant="outlined" color="primary" onClick={() => setOpen2(true)}>
        Open dialog using custom Paper
      </Button>
      <StyledDialog
        onClose={() => setOpen1(false)}
        aria-labelledby="simple-dialog-title"
        open={open1}
      >
        <DialogTitle id="simple-dialog-title">
          Paper styled via child selectors
        </DialogTitle>
      </StyledDialog>
      <StyledDialog2
        onClose={() => setOpen3(false)}
        aria-labelledby="simple-dialog-title"
        open={open3}
      >
        <DialogTitle id="simple-dialog-title">
          Paper styled via MuiDialog-paper
        </DialogTitle>
      </StyledDialog2>
      <Dialog
        onClose={() => setOpen2(false)}
        aria-labelledby="simple-dialog-title"
        open={open2}
        PaperComponent={StyledPaper}
      >
        <DialogTitle id="simple-dialog-title">
          Paper styled via custom Paper component
        </DialogTitle>
      </Dialog>
    </div>
  );
}

