Slight addition using wider, shadowy gradients to conceal some aliasing issues:

    td.ind > img { opacity: 0 }
    td.ind {
        background: 
            linear-gradient(to left, rgba(246,246,240,1) 0px, rgba(246,246,240,1) 14px, rgba(246,246,240,0) 14px),
            repeating-linear-gradient(to right, rgba(0,0,0,0) 0px, rgba(0,0,0,0.03) 39px, rgba(0,0,0,0) 40px);
     }

Screenshot: https://i.imgur.com/f2WfHyp.png

Unfortunately it breaks on the 'threads' page.