When using the resize CSS property, the default diagonal lines appear in the corner of the element. Everything about this small space is created by the browser--without any input from the site author or site user. So, if both the site author or user have poor vision, they will not be able to see the resize icon, much less click-and-drag to change the size of the HTML element. One solution would provide multiple options much like the CSS cursor alternatives (though, probably not as many) to aid different types of disability as well as provide a way for the site authors to associate their resize icon via an image (also like the cursor CSS property).
<rdar://problem/28244889>