This is a modified version of slimbox, with a iframe support added.

Find:

this.eventPosition = this.position.bind(this);

Add a new line after it:

this.body = top.document.body;

Find:

.injectInside(document.body)

Replace with:

.injectInside(this.body)

Done.

Modified slimbox.js file can be download here:

[attach=140]