SimpleContainer should throw IllegalArgumentException (with a message saying you don't support this) if size is called with a percentage size, currently it accepts the setSize method call and it gives no indication that it isn't supported.
Also HtmlLayoutContainer here to it would be good know what this can't do, ideally by throwing a runtime exception if possible but if not at least the docs should indicate this.
HtmlLayoutContainer does not extend resizecontainer and so it does not handle any resizing. This is the same with FlowLayoutContainer. However, we probably can also add notes that it does not resize its children (although, how should it be able to do it, as no HtmlLayoutContainer equals another. They can all have different markup)