It looks like the widgets on the home page there may not play nicely since they don’t have unique ID’s. You might try the BlackStudio TinyMCE plugin which adds a widget with the editor from the page/post screen. It does have proper ID’s to hook styling to.
With the widgets that are there now, you can make them full width this way:
.home-lower .widget_wysiwyg_widgets_widget {
width: 100%;
}
WordPress doesn’t have a built in filter for the widget classes that we can use to choose a width from a drop-down inside the widgets. I could add one to a custom widget that’s in a theme, but it wouldn’t help out widgets added via a plugin or the ones in the WordPress core itself.
Hope that helps out,
Bill