Branding a page to look like the rest of the site is easy to do with SharePoint Designer. If you have a page that you created from scratch or in which you copied the content from a different site or from a document, you can easily provide that page the matching look and feel for the rest of the site by attaching the Master Page of that site to it.

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Master Pages are used to create a consistent layout of pages on a SharePoint site. Watch this video to better understand how they are used and where they are stored on a site