Tests associated with a test plan UI breaks when having a large number of tests

Description
Tests associated with a test plan UI breaks when having a large number of tests

Pre-conditions

How to reproduce

1. Add additional fields to the edition screen of test plans:
   
   (example)
2. Create a Test Plan and add a group of Tests (30+)
3. Edit the Test Plan

Actual result/Attachments

Expected result
The custom field section should be correctly aligned and with no tests outside of the box.

Version

• 6.2.4