jQuery Tools Scrollable: add a class to focused item

Question

I'm using the jQuery Tools Scrollable plugin to scroll through some items horizontally.

I want to add a class to the focused item in a Scrollable instance. I've determined that could add an '.active' class to the focused item onSeek, and onBeforeSeek I would remove '.active' from the item that has it, but I'm having trouble writing the function. onSeek and onBeforeSeek are events for the plugin.

I'd appreciate any help! Thanks!