I have tried to make a transparent GIF before.
For a while, the GIF code looked like this:
<img id="im" class="ctx-gif" src="//i.imgflip.com/739jne.gif" alt="image tagged in gifs,bugs,glitch,transparent,watermark | made w/ Imgflip images-to-gif maker">
It displayed a .gif file, meaning that transparency would remain, as .gif supports transparency, and also made it possible to specify a background color.
However, once it was featured, the code looked like this:
<video disableremoteplayback="" muted="" loop="" playsinline="" id="vid" class="ctx-gif" data-src="//i.imgflip.com/739jne.gif" poster="//i.imgflip.com/2/739jne.jpg">
<source src="//i.imgflip.com/739jne.mp4" type="video/mp4">
<p>Your browser does not support html5 :(. If you believe you received this message
in error, please email
[email protected] and tell us what browser you're using!</p>
<p>GIF Watermark In Pieces | THEN THE WATERMARK WILL BE IN PIECES. IF YOU MAKE A TRANSPARENT GIF, | image tagged in gifs,bugs,glitch,transparent,watermark | made w/ Imgflip images-to-gif maker</p>
</video>
It now displayed a .mp4 file, meaning that transparency would be gone, as .mp4 does NOT support transparency.
In short, the .mp4 file is causing this. However, if we could choose between the files, and we selected the .gif file, rather than the .mp4 file, and if .gif was selected, the site used the first code instead of the second code, then we could preserve the transparency.