The easy web builder is based on the front-end framework UIkit. This means HTML written in easy website builder, like the page layouts, is using classes and attributes from UIkit. They are prefixed with
uk- so that they can easily be identified. The style customizer allows you to modify the UIkit CSS inside the easy website builder. Meanwhile, elements in the builder are based on UIkit components, like the Slideshow element which is built on the Slideshow component.
All UIkit features are available when writing custom markup or starting child theme development for the easy website builder. There is also a comprehensive documentation for UIkit. It could be regarded as a more technical extension of the easy website builder documentation.