Type ./src in the App location box.

[zen37]

Select Custom from the Build Presets dropdown.
Type ./src in the App location box.
Leave the Api location box empty.
Type ./src App artifact location box.

It should be:

Select Custom from the Build Presets dropdown.
Type / in the App location box.
Leave the Api location box empty.
Type / App artifact location box.

[rochabr]

Thank you for pointing this out, @zen37. The location of the webpage code will depend on how you setup your code structure. In this case it is on the root folder.