idex.html

<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
    <link rel="stylesheet" href="style.css" />
  </head>
  <body>
    <div class="b1">
      <button id="plus">+</button>
      <div id="number">1</div>
      <button id="minus">-</button>
    </div>

    <button id="b2">click to change color</button>
    <div id="div2"></div>

    <button id="b3">hide</button>
    <div id="div3"></div>

    <button id="b4">click random color</button>
    <div id="div4"></div>

    <div id="all">
      <div id="b5">Do you like me</div>
      <div id="yes">Yes</div>
      <div id="no">No</div>
      <div id="ccc">I know it!!</div>
    </div>

    <script src="aa.js"></script>
  </body>
</html>