The source folder in the portals repo is currently named dev. It should be renamed to src to align with the more popular web-development conventions.
This change should make this repository easier to understand for new contributors. Also, it will free up the folder name dev for a different and more appropriate purpose: storing the compiled but un-minified build products (this is a separate patch however, as it includes substantial changes to the Gulp build pipeline).
Changing the folder name is not as simple as it sounds though, it does require replacing the name in the Gulp build process too. This task should wait until a separate config.js file has been created as part of T277405.