fix(Data Mapper): Increase the connection area at the end of a property point

[Elaina-Lee]

• Please check if the PR fulfills these requirements

• The commit message follows our guidelines

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
  css change
• What is the current behavior? (You can also link to an open issue here)
  connection area radius: 10px
• What is the new behavior (if this is a feature change)?
  connection area radius: 15px
• Does this PR introduce a breaking change? (What changes might users need to make in their application due to this PR?)
  no
• Please Include Screenshots or Videos of the intended change: