add some more custom config and put every thing in comment in the custom.yaml template
/*
YUI 3.10.3 (build 2fb5187)
Copyright 2013 Yahoo! Inc. All rights reserved.
Licensed under the BSD License.
http://yuilibrary.com/license/
*/
.yui3-g{letter-spacing:-0.31em;*letter-spacing:normal;*word-spacing:-0.43em;text-rendering:optimizespeed}.opera-only :-o-prefocus,.yui3-g{word-spacing:-0.43em}.yui3-u{display:inline-block;zoom:1;*display:inline;letter-spacing:normal;word-spacing:normal;vertical-align:top;text-rendering:auto}#yui3-css-stamp.cssgrids-base{display:none}