You can override a View with a Visualforce page and add style sheet on this page.
here is the sample code of visualforce page with CSS
<!-- custom Stylesheet -->
<apex:detail/> <!-- this tag will display standard detail pages as defined by the associated page layout for the object in Setup -->
Here are the steps to link above create page with custom object view link.
- For custom objects, from Setup, click Create | Objects, and
select custom objects in the list.
- Click Edit next to the View
- Pick the type of override you want associated with the
- Select the Visualforce page you want to run when users
click the view button.
- Click Save.