(Trying a new theme, btw. Jury out at the moment.)
The goal was to understand the absolute minimum effort required to get the Helvtica/Arial style typefaces from BootStrap to display. The answer:
<html> <head> <link rel="stylesheet" href="http://maxcdn.bootstrapcdn.com/bootstrap/3.2.0/css/bootstrap.min.css"> </head> <body> <h1>H1 in BootStrap</h1> <h2>H2 in BootStrap</h2> <h3>H3 in BootStrap</h3> <h4>H4 in BootStrap</h4> <h5>H5 in BootStrap</h5> Body in BootStrap </body> </html>
W3Schools helped, as ever.