This is element x. It has inline style border: 1px solid #cc0000.
Element y is the test style sheet.
y.addRule('pre','font-size: 150%')
y.deleteRule(y.cssRules.length-1)
y.insertRule('pre {font-size: 150%}',y.cssRules.length)
y.removeRule(y.rules.length-1)