Take a look at our FAQs here: https://software.intel.com/en-us/xdk/faqs/app-designer
In particular Q3: How do i size UI elements in my project?
We also have a video created by one of our engineers on responsive design layout (part 3) here: https://software.intel.com/en-us/search/site/field_platform/html5-42008/field_tags/intel-xdk-42296/language/en/type/bds_video?query=app+designer&sort_by=search_api_relevance&sort_order=DESC&collapsed_state=null
