In JQuery 1.6.1, we can supposedly use += or -= with css() just as we can do with animate(), but this isn't working. Does anyone see a problem with the code?

$(document).keydown(function(e) {  
    if (e.which == 37) { //37 left arrow key.
        $('div').css('left', '-=10px')
    }
});

Check http://jsfiddle.net/QLFEy/3

javascript jquery css jquery-1.6
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