I created react app react router 4.but I build my project using npm run build route URL not working and display 404 page.how can I fix that? I have no idea.this is my code

import React from "react";
import ReactDOM from "react-dom";
import registerServiceWorker from "./registerServiceWorker";
import { BrowserRouter as Router,Switch,Route } from "react-router-dom";

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

import "react-datepicker/dist/react-datepicker-cssmodules.css";
import "./styles/main.scss";


import App from "../App";
import AdminHome from "../pages/admin/home";
import Login from "../pages/login";
import PrivateRoute from "./privateRoute";

const theme = createMuiTheme({
    palette: {
        type: "dark"
    }
});


ReactDOM.render((
    
        
            
                
                
                
                 
Not Found
}/>
            
        
    
), document.getElementById("root"));

registerServiceWorker();

Can anyone help me to fix this?