OK – you’ve created that great new ASPX page on your site (using SharePoint Designer 2010), and when you preview the page in the browser, you noticed that it doesn’t have a master and it doesn’t match your existing site. Well, it’s not that hard to make it happen, after all.
All you need to do is click on the file name under the Site Pages section of the Site Objects Window. then, in the Page Tab (in the Ribbon Menu), click on Edit/Edit File in Advanced Mode.
Once you’re there, click on the Style tab in the Ribbon menu, and look over to the left for the Master Page section. Click on ‘Attach’ and then ‘More Options’. A dialog comes up with all your possibilities. Just choose which Master Page you want, then, in the next dialog just confirm that the part of the page matches the ContentPlaceholder from the Master Page, and there you go!
All Things DotNet Discussed – Winforms/ASP.Net/SharePoint/WPF