In order to access the advanced survey customization features, you will need to enable survey wide javascript, the javascript item, and survey wide CSS for your application. These features are included in Checkbox for all plans and editions with the exception of the Checkbox Online Basic plan.
Adding javascript and altering the CSS of a web page can have negative effects on the functionality of your survey including the chance that it could inadvertently prevent users from being able to complete their responses. We strongly recommend that any javascript or CSS modifications made to your surveys be done by someone with detailed knowledge of javascript and CSS. We also suggest that they review the documentation on this site regarding the item or section of the survey that they are attempting to manipulate or extend.
Unfortunately, if there are any survey issues caused by custom javascript or CSS our support team will not be able to assist in resolving those issues.