I'm not sure how the templates are generated, but the installed localbattery.html (2.5.47) contains:
<head>
...
<link rel='stylesheet' href='static/css/default_style.css' type="text/css">
</head>
This refers to default_style.css after an experiment's style.css making it awkward to override styles (e.g. experiment background colour). As the canonical config.json includes default_style.css before style.css it looks like the reference in the template should be removed.