The UI is dressed up using Tailwinds CSS, used primarily to get a feel for this popular CSS utility library.
For keeping track of basic data such as a weight number, date, and userId, a fancy relational SQL database isn't really needed. I chose Firebase, a cloud-based NoSQL database from Google. Google has excellent secure authentication, and the database provides real-time updates for user data. Combined with D3, you'll see the graph visualization triggered with any update such as adding or deleting.