Why is it when I link files (example would be a CSS file in an aspx page) in Visual Studio (localhost), I have to add the project name in the link for it to work?

Example:
<LINK href="/PROJECTNAME/includes/styles.css" type="text/css" rel="stylesheet">

instead of using the right way:
<LINK href="../includes/styles.css" type="text/css" rel="stylesheet">

How can I correct this?