Unwanted empty border in WebGL minimal template

I believe I've realized where these spaces are coming from: default HTML styling.

From how I understand it, Unity's "Minimal" WebGL template is not just a simply designed template, it's basically no template at all. When a web browser loads the Unity project, it looks for a style guide to tell it how to display the elements on the page. When it finds none, it references it's own style guide (which seems to be fairly standard across the major browsers at this point) by default. It so happens that the typical default style guide currently includes a margin of 8 pixels, and this is basically what causes that buffer around the edges (default top-left alignment also contributes to the problem). It kind of makes sense for totally blank web pages, but it starts to look wonky once it's embedded in a more complex layout like the one that itch.io uses.

So, we can blame Unity for making their "Minimal" template too minimal, itch.io for not implementing robust formatting features, or ourselves for trying to publish games to the Web without knowing a shred of HTML/CSS in the first place.

In any case, the solution I've gone with for now is creating a custom template based on the Default template and just taking out the code and resources for the footer bar. I've attached a .zip with the template I use and instructions for how to use it / add it to Unity.

I hope this helps!