For the layout XPages focus on the web development standards HTML and CSS. Additionally themes can be used as an easier way to manage multiple CSSs. XPages comes with default themes, for example the OneUI theme.
In addition to client side logic Dojo can also be used for rich user interface widgets and charts.
Access to Backend Services
As any web application XPages applications can use REST services. XPages also provides easy mechanisms to bind data sources to UI controls so that for many scenarios no code needs to be written. Additionally XPages allows to declaratively only refresh parts of the page via Ajax when submitting data.