In case anyone else is trying to do this, I successfully embedded the video using this raw HTML:

<div class="video-wrapper">
  <video controls>
    <source src="/your-video.mp4" type="video/mp4">
    <source src="/your-video.webm" type="video/webm">
    Your browser does not support the video tag.
  </video>
</div>

With the following added to the raw htnl addon's Custom CSS:

.video-wrapper {
  max-width: 100%; /* Or a specific max-width if you don't want it to exceed a certain size */
  margin: 0 auto; /* Centers the wrapper if it has a max-width */
}

.video-wrapper video {
  width: 100%; /* Makes the video fill the width of its parent */
  height: auto; /* Automatically calculates height to maintain aspect ratio */
  display: block; /* Removes extra space below the video tag */
}

Dan

Source: Gemini