set dark mode using react hooks typescript

React beginner here, english is not my mother language sory for mistakes, i have been looking for setting dark mode on my website, examples what i have seen are mostly toggle between dark and light and you need to specify each colors inside those two. My point is how can i toggle between dark and light(this light should be my default colors set in css)

In my components each has its own css(own colors).If i want to have dark mode which toggles between dark and default css, for example changing background color, how would it be ?

my code:

import React, {useState, useEffect } from "react";

...

<div className="app">
      <Switch>
         <Route path="/a">
          <A />
        </Route>
        <Route path="/c">
          <C />
        </Route>
        <Route path="/b">
          <B />
        </Route>
        <Route path="/">
          <Redirect to="/a" />
        </Route>
      </Switch>
    </div>

if need more information, i can give.