react-router doesn't work when I refresh the browser

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react-dom.min.js"></script>


import React, { Component } from 'react'
import { BrowserRouter as Router, Route, NavLink } from 'react-router-dom'

import { HashLink } from 'react-router-hash-link'

import Homepage from '../homepage/homepage'
import Sas from '../sas/sas'

const Routes = () => {
    return (
<Router>
    <div>
        <nav className="navbar fixed-top navbar-expand-sm navbar-light bg-white py-3">
         <NavLink className="navbar-brand right-border-menu px-5" exact to="/">Statuts Juridiques</NavLink>
         <button className="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarNavAltMarkup" aria-controls="navbarNavAltMarkup" aria-expanded="false" aria-label="Toggle navigation">
             <span className="navbar-toggler-icon"></span>
  </button>
  <div className="collapse navbar-collapse flex-row-reverse" id="navbarNavAltMarkup">
      <div className="navbar-nav">
             <NavLink className="nav-item nav-link" exact to="/sas">Je crée mon entreprise</NavLink>
   </div>
 </div>
</nav>

<Route path='/' exact strict component={Homepage} />
<Route path='/sas' exact strict component={Sas} />

   </div>
 </Router>
    )
}

export default Routes

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react-dom.min.js"></script>

import React, { Component } from 'react'

class Sas extends Component {
  
  render() {
return(
  <div className="column justify-content-center align-item-center my-5 py-5">
   
   Sas page
    
  </div>
)
  }
}
 
export default Sas