How to fix high Draw Calls when using external HTML code?

Hello. So my problem is related to the external HTML page that I'm using in my game.

I've made custom Admin dashboard for the game (vanilla HTML+CSS+JS).

And when I called it from the game (as the overlay, above the game itself), the draw calls in the inspector(that debug menu) jumped highly and CPU usage was about 94%. I would like to know how to fix that. And why it's happening? Thanks in advance!

HTML content shouldn't affect the draw calls measurement, as draw calls are the time spent drawing things in to the canvas, and HTML content isn't drawn in to the canvas. So this doesn't make sense. It would be easier to help if you could make a minimal project demonstrating the issue.