What are the three primary parts of responsive design theory?

Three Primary Parts of Responsive Design Theory

• Flexible Layouts: Use a flexible grid to create the website OR HTML page layout that will dynamically resize to any width depending on device sizes like Desktop, Laptop, Mobile Phone, etc.
• Media Queries: An extension to media types when targeting and including styles. The media queries allow designers to specify different styles for specific browsers and device circumstances.
• Flexible Media: Makes media (like Images, Video, and other formats OR HTML elements) scalable, by changing the size of the media as the size of the viewport changes.

Responsive Web Design 

It is an approach to designing a web page. That makes web pages render well on a variety of devices (Mobile, Desktop, and Laptop) and Windows (OS) or screen sizes. Responsive layouts automatically adjust and adapt to any device screen size, whether it is a desktop, a laptop, a tablet, or a mobile phone.

For Example of Responsive Website Design

A responsive website automatically changes to fit the device you're reading it on when a website is designed fully responsive. The layout and/or content responds or adapts based on the size of the device screen they are presented on. 

How to Design a responsive HTML web page? OR What is the process to design a responsive HTML page? 

• Adds responsive meta tags in your HTML document OR web page.
• Apply media queries to your layout through the CSS.
• Make Images and Embedded Videos Responsive.
• Ensure your typography will be easily readable on mobile devices.