Create a comments popup only with the top section (displaying details of the selected item)
When the popup loads, the webapp retrieves data from the selected API and shows details about the selected item.
Add event to button prepared by your teammate that will open your popup. You need to communicate with your team member to make sure that you do not block each other (most likely the easiest solution is to merge the list of items feature to the dev branch before you try to add that event).
Find an API to base the development of the webapp around it. The API should allow you to
Get a list of items with a unique item id (or generate the unique id).
For a given item, get detailed information about it.
choose an APIs that doesn't need authentication. if you select an API that requires authentication, you should implement it on your own. Also, if you select an API that provides image resources your webapp will be more visual.
Create a reservations popup only with the top section (displaying details of the selected item)
When the popup loads, the webapp retrieves data from the selected API and shows details about the selected item.
Add event to button prepared by your teammate that will open your popup. You need to communicate with your team member to make sure that you do not block each other (most likely the easiest solution is to merge the list of items feature to the dev branch before you try to add that event).