Added CSS border.
Added CSS border.

Used to show how the browser knows where the image will render and can
continue with the layout while the image loads. Once it's loaded,
there's no need to redraw the page.

alanwsmith/doc-write-image-loader,alanwsmith/doc-write-image-loader,alanwsmith/document.write-image-loader,alanwsmith/doc-write-image-loader,alanwsmith/document.write-image-loader