Reuse shared HTML markup with layouts

- [Instructor] Navigate around the Explore California site … a little bit and notice … how every single page contains the same common sections … such as the header, footer … and even the left side bar section of the page. … This is a great thing as it gives a consistent look … and feel throughout the site. … However, it's really painful … to change each instance of those common elements … across all pages in the site. … Luckily ASP.NET Core MVC allows us … to define special Razor pages … whose sole purpose it is … to define this common layout … and render content from individual pages … inside of this layout. … These types of Razor pages are referred to as layouts … and they're a great candidate to live … in that shared views folder … we saw ASP.NET Core MVC looking for earlier. … To demonstrate how they work, … let's create the new Shared folder under the Views folder. … Then I'll make a copy of our index.cshtml page … into this new Share folder … and rename it _Layout.cshtml. … Now there's nothing special about the underscore …