StyleBundle - Combine CSS Files in ASP.NET MVC

Here you will learn how to combine multiple CSS (Cascading Style Sheet) files to return it in a single HTTP request.

ASP.NET MVC API includes StyleBundle class that does CSS minification and bundling. Same as the script bundle, all the style bundles should be created in the BundleConfig class. under the App_Start folder.

The following example shows how to combine multiple CSS files into a bundle.

Example: Create Style Bundle

public class BundleConfig
{
    public static void RegisterBundles(BundleCollection bundles)
    {            
        bundles.Add(new StyleBundle("~/bundles/css").Include(
                        "~/Content/bootstrap.css",
                        "~/Content/site.css"
                    ));
        // add ScriptBundle here..  
        
    }
}

In the above example, we created a new style bundle by creating an instance of the StyleBundle class and specified the virtual path and bundle name in the constructor. The ~/bundles/ is a virtual path and css is a bundle name. Then, we added two .css files, bootstrap.css, and site.css in this bundle. The bundles.Add() method is used to add new bundles into the BundleCollection. By default, the above css bundle will be created in the release mode. Use BundleTable.EnableOptimizations = true if you want to see bundles in the debug mode.

Now, to include the above css bundle in your webpage, use Styles.Render() method in the layout view, as shown below.

Example: Include Style Bundle in View

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>@ViewBag.Title - My ASP.NET Application</title>
<meta property="og:title" content="@ViewBag.Title - My ASP.NET Application" />
<b>@Styles.Render("~/bundles/css")</b>
</head>
<body>
    @Styles.Render("~/bundles/css")
</body>
</html>

Now, when you run the application in the release mode, you will see the bundle is created and loaded in a single request.

You can use the IncludeDirectory() method, version wildcard {version}, and CDN path the same way as ScriptBundle. Learn how to set image path in StyleBundle.

ASP.NET MVC framework calls the BundleConfig.RegisterBundle() from the Application_Start event in the Global.asax.cs file. So, all the bundles are added into the BundleCollection at the starting of an application.