You can edit / change the code and click run button <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> <style> h1 {font-size: 15mm;} h2 {font-size: 10mm;} p { font-size: 5mm; line-height: 10mm; } </style> <script>var clicky_site_ids = clicky_site_ids || []; clicky_site_ids.push(101319977);</script><script async src="//static.getclicky.com/js"></script> <h1> My font-size is 15mm</h1> <h2> SnoopCode - My font-size is 10mm</h2> <p>My font-size is 10 mm</p>