how to get rid of a padding in a material ui container component?

The disableGutters prop removes the padding.

Example:

import React from "react";
import CssBaseline from "@material-ui/core/CssBaseline";
import Typography from "@material-ui/core/Typography";
import Container from "@material-ui/core/Container";

export default function SimpleContainer() {
  return (
    <React.Fragment>
      <CssBaseline />
      <Container disableGutters maxWidth={false}>
        <Typography
          component="div"
          style={{ backgroundColor: "#cfe8fc", height: "100vh" }}
        />
      </Container>
    </React.Fragment>
  );
}

Related documentation: https://material-ui.com/api/container/#props