Steps:

1. Go to Page
2. Click [+] and choose Landing Page
3. Choose layout and confirm
4. Drag and drop for ex. code block
5. Fill the content field and on design tab type fill the fields with a typo in Style field, for example:
Class: cls
_.cls

_
6. Click Submit

Actual result:

Error 500 in block modal is shown: parse error: failed at `background: blue color: white;} }` (stdin) on line 1

Expected result:

User friendly message