Added the Structure and the styles to a Toogle Button for allow the dark mode

src/components/Header.jsx

@@ -1,4 +1,5 @@
 import React, {useState} from 'react'
+import DarkMode from './DarkMode'
 import HeaderButton from './HeaderButton'
 
 const Header = () => {
@@ -10,6 +11,7 @@ const Header = () => {
         <header className="header-main-page">
             <a href="/"><h1>Pomodoro Timer</h1></a>
             <h3>Made By <span className="selectable"><a target="_blank" href="https://www.behance.net/franpessano" rel="noreferrer">Francisco Pessano</a></span></h3>
+            <DarkMode />
         </header>
     )
 }