They have some really impressive documentation in this project. It's really great. They go over their browser support here: https://designsystem.digital.gov/do

They have some really impressive documentation in this project. It's really great. They go over their browser support here: https://designsystem.digital.gov/documentation/developers/ https://designsystem.digital.gov/documentation/developers/ "We’ve designed the Design System to support older and newer browsers through progressive enhancement. The current major version of the Design System (1.0) is designed to support the newest versions of Chrome, Firefox, Safari, and Internet Explorer 9 and up. The next major release (2.0) will follow the 2% rule: we will officially support any browser above 2% usage as observed by analytics.usa.gov. Currently, this means that the Design System version 2.0 will support the newest versions of Chrome, Firefox, Safari, and Internet Explorer 11 and up."