1.4.4 Non-Conformance Shown with Non-Technical Explanation
The above heading overruns the page side when zoomed to 200% because the heading uses a fixed font size.
1.4.3 Non-Conformance CSS Markup and Technical Details
{font-size:128px;}
The font-size should be defined in relative rather than absolute terms. One way of doing that would be to use em (measured relative to the default font size, 2em would 2 times the font size) rather than px.