NOT:

<div>Play video</div>

USE CORRECT ELEMENT:

<button>Play video</button>

<img src="dinosaur.png">

<img src="dinosaur.png"
     alt="A red Tyrannosaurus Rex: A two legged dinosaur standing upright like a human, with small arms, and a large head with lots of sharp teeth.">

<img src="dinosaur.png"
     alt="A red Tyrannosaurus Rex: A two legged dinosaur standing upright like a human, with small arms, and a large head with lots of sharp teeth."
     title="A red dinosaur">


<img src="dinosaur.png" aria-labelledby="dino-label">

<p id="dino-label">The Mozilla red Tyrannosaurus Rex: A two legged dinosaur standing upright like a human, with small arms, and a large head with lots of sharp teeth.</p>

<img src="logo.png" alt="">

<form>
  <div>
    <label for="name">Fill in your name:</label>
    <input type="text" id="name" name="name">
  </div>
  <div>
    <label for="age">Enter your age:</label>
    <input type="text" id="age" name="age">
  </div>
  <div>
    <label for="mood">Choose your mood:</label>
    <select id="mood" name="mood">
      <option>Happy</option>
      <option>Sad</option>
      <option>Angry</option>
      <option>Worried</option>
    </select>
  </div>
</form>

<header>
  <h1>...</h1>
  <nav role="navigation">
    <ul>
    	<li tabindex="0">Example</li>
        <li tabindex="0">Example</li>
    </ul>
    <form role="search">
      <input type="search" name="q" placeholder="Search query" aria-label="Search through site content">
    </form>
  </nav>
</header>

<main>
  <article role="article">...</article>
  <aside role="complementary">...</aside>
</main>

<footer>...</footer>

<ul role="tablist">
  <li class="active" role="tab" aria-selected="true" aria-setsize="3" aria-posinset="1" tabindex="0">Tab 1</li>
  <li role="tab" aria-selected="false" aria-setsize="3" aria-posinset="2" tabindex="0">Tab 2</li>
  <li role="tab" aria-selected="false" aria-setsize="3" aria-posinset="3" tabindex="0">Tab 3</li>
</ul>
<div class="panels">
  <article class="active-panel" role="tabpanel" aria-hidden="false">
    ...
  </article>
  <article role="tabpanel" aria-hidden="true">
    ...
  </article>
  <article role="tabpanel" aria-hidden="true">
    ...
  </article>
</div>