That sounds like your app may have custom styling that is clashing with how the Bizzomate Gannt widget is working.
You can try using your web browser's Inspect Element tool and see what styles are being applied to that element. You may well see that your app's classes are being applied first and causing the issue.
If this is the case, you will probably need to find the clashing class and make that selector more specific in your app so it doesn't clash with the widget.
Good luck!