How to create modal popup window with grayed background on page load

HTML (HyperText Markup Language) is the main markup language for creating web pages and other information to be displayed in a web browser, providing both the structure and content for what is sent from a web server through the use of tags. The current implementation of the HTML specification is HTML5.

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The successor to Active Server Pages, ASP.NET websites utilize the .NET framework to produce dynamic, data and content-driven web applications and services. ASP.NET code can be written using any .NET supported language. As of 2009, ASP.NET can also apply the Model-View-Controller (MVC) pattern to web applications