The reported behavior is caused by the fact that the base styles for the controls are loaded after your custom styles. Your styles are overridden by the base ones, thus breaking the custom layout.
In order to overcome this issue, you would need to define stronger CSS selectors for your styles which would prevent the base styles from overriding them.
And last, but not least, I would suggest you to vote for the following Feedback Portal item
feature request, which is for adding the ability to control the styles loading order to avoid such an issue much easily.
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Feedback Portal
and vote to affect the priority of the items