We recently let our intern create multiple copies of our application using other frameworks. While they were busy doing that, we decided to write the update using just the ArcGIS JavaScript API. The Y2K society checked out our app and approved our changes, but that wasn't all they had to say.
When we met with the Y2K society board, we found a critic in a new member of the board. They thought it looked okay, but it needed a more modern look. When asked for details, they showed us websites on their tablet that they thought looked good. All the sites we were shown had one thing in common, they were all built using Bootstrap. He managed to convince others on the board that our app needed to embrace this new style.
Going back to the drawing board, we looked at what ESRI had to offer. We decided to incorporate ESRI-Bootstrap into our application. It provides a modern feel.