Same Aspx Code When I Write In Sharepoint Webpart Page Design Gets a slight differ

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CSS

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SharePoint2010

Hi all Tech geeks avilable here in the forum,
I am facing some strange problem. I have a aspx page in .net
I just wanted to write the same html code in a sharepoint webpart(same as application page in .net) due to some requirement but doing so i am facing some starnge problem all the design is comming same but the fonts are little increased n size which causing a little differ in style/look of that page.
I cant understand the problem as the whole code is same and all css reference are also same just it has been written in a application page rather than a normal .net web page

kindly copy and paste following link to see the changes in the page

http://postimg.org/image/p3f79a02f/[^]