There is some inline CSS on the forum pages:
/* CSS: bbo_handviewer*/ .hv_frame { border: 0; float: left; padding-right: 0.2em; /* Separate diagram from text */ padding-top: 0.4em; /* Separate one diagram from another */ }
Any chance you can add:
.hv_frame iframe {max-width:100%;}
Then on my screen it'll scale down to fit (it'll add whitespace underneath since it has a fixed height rather than scaling responsively, but at least it'll be readable).