If you have done heavy styling,  bad CSS codes can slow down your page loading. It can also cause Browser crash. you should consider optimizing css.

Here is a very nice Presentation by Jon Rohan about improving Css Performance.

Few of his main points are:

• Manipulating the Dom, CSS Animation and User actions cause style recalculation and it’s very bad deadly for browser.
• There shouldn’t be unnecessary identifier , ancestor,  universal selector, unqualified selector and  chaining in CSS.
• Unnecessary HTML should be removed
• Refactor CSS into reusable components.

Check out this beautiful presentation :