CSS also affects other web sites

[vandelay]

First, thanks for this extension.

We use a commercial web site which also uses CSS class number and they were appearing in darkorange on my machine as the CSS in this extension overrides the styling on the site.

[grahamb]

Also seeing this when using semantic-ui; I have an icon with class .key.

Your CSS should be namespaced to prevent collisions like this, and ideally (don't know if this is possible with Safari's extension APIs) only active when viewing actual JSON.