<html><head><script src="https://libs.baidu.com/jquery/2.1.4/jquery.min.js"></script><script>$(document).ready(function(){ $("button").click(function(){ $("p").css("border-width", function(i){ return i + 25; }); });});</script></head><body><button>Change the border-width property of the p element</button><p style="border: 1px solid black;">This is a paragraph.</p></body></html>