<html><head><script src="https://libs.baidu.com/jquery/2.1.4/jquery.min.js"></script><script>$(document).ready(function(){ $("button").click(function(){ $("div").width(function(n, c){ return c - 200; }); });});</script></head><body><button>Decrease width of div with 200 px.</button><br><br><div style="height:100px;border:4px solid;"></div></body></html>