The Cabanova website builder editing environment uses Adobe Flash technology. When you publish your website it is saved in both Flash and HTML5 formats.
If the browser displaying your published website does not have a Flash plugin installed, the HTML5 version will be displayed. Depending on the computer and the software installed the site may not look exactly the same as in Flash. This is because HTML5 is still a relatively new technology and is not fully supported on all browsers yet. The various browsers have also implemented the features in different ways.
To name a few examples, not all HTML5-compatible browsers support drop shadows yet, and the text in your pages may look slightly different because each browser/operating system has a different engine for rendering fonts.
If you are used the cross-platform consistency that Flash has provided through the years, you will have to get used to the fact that this is something that HTML5 will not be able to match. These differences are very minor though, and most people visiting your website will never know the difference. The important thing is that with HTML5, your website can be displayed on modern mobile devices that do not support the Flash plugin (e.g. iPads and iPhones).