<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>HTML & JS Calculator</title>
  </head>
  <body>
    <h1>Welcome to the best calculator out there!</h1>

    <main id="mainContent">
      <form action="#" onSubmit="event.preventDefault(); calculate();">
        <h2>Enter two numbers:</h2>
        <div>
          <input type="n