2500x is a tongue-in-cheek web-based graphic format that converts a raster image to a series of pixels coded in HTML and CSS. Its name derives from the possibility that the file size will multiply by as much as 2500 times the original image size. In a reasonably modern browser, if the browser doesn't crash first, the graphic will display losslessly as a faithful rendition of the original.
Each pixel is in the form
<p style="color:rgb(229,218,226)">.</p>, with a single period in a paragraph with inline style giving an RGB color value. The entire thing is within these DIVs:
<div id="twofiveoo" class="backdrop twofiveoo pb-5 sneakattack" style="visibility: visible;"><div> ... </div></div>
The site stylesheets in the
http://not-png.xyz/ site cause this code to render in a format that displays the graphic.