current head of develop:
% cd examples/newsboxes
% mojito build html5app /tmp/nb
% grep rel= /tmp/nb/index.html
<link rel="stylesheet" type="text/css" href="static/Frame/assets/reset.css"/>
<link rel="stylesheet" type="text/css" href="static/Shelf/assets/shelf.css"/>
untested, but looks like adding the traing slash here will break these links