Does low-power mode on iOS11 impact pseudo-elements that modify Shadow DOM elements?

Question

In normal power mode, on iOS11 (tested on iPhone 8 and X), I am able to hide a button element overlay inside the shadow root of a video element.

Once low power mode is enabled, my pseudo-element is no longer able to hide the button element overlay. What's going on? How can I hide the button element in low power mode?

My CSS

// Placed outside Shadow DOM in my SCSS file.    
video::-webkit-media-controls-start-playback-button {
  display: none !important;
}

DOM element to be modified

<video style="display: inline;" class="playerElement" poster="" autoplay="true" width="100%" oncontextmenu="return false;">
  // Shadow Content (User Agent)
  <style>
    // Lots of default styles with Apple legal language.
  </style>
  <div class="media-controls-container">
    <div pseudo="-webkit-media-text-track-container" class="visible-controls-bar" style="display: none;"></div>
    <div class="media-controls inline ios uses-ltr-user-interface-layout-direction" style="width: 375px; height: 275px;">
      <button class="play-pause paused center" aria-label="Play" style="width: 11px; height: 13px; left: 16px;">
        <div class="background-tint">
          <div class="blur"></div>
          <div class="tint"></div>
        </div>
        <picture style="width: 11px; height: 13px; -webkit-mask-image: url(data:image/svg+xml;base64,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);"</picture>
      </button>
    </div>
  </div>
</video>

Note: This issue occurs on Safari, Chrome, and Firefox on iOS11. Pseudo-element works fine on iOS10 (tested on iPhone 5s).

Answer 1

This is a pretty rare occasion since a majority of iOS users don't use iOS 11 anymore. However, I believe this happens because of how the low power mode works. Usually, low power mode turns off unnecessary graphics, animations, or visual effects in general. Judging from what happened to you, the operating system must've thought your pseudo-element was an unnecessary effect and decided to remove it. In iOS 11, low power mode was still a pretty new thing, so it probably still had incomplete testing.

I wouldn't say my answer is a completely reliable answer, but this is basically what I believe is the reason for your problem.

(once again, please don't completely trust my answer, I'm not a full professional at this stuff.)