In a symmetrical grid, the right page will be exactly the opposite of the mirror image of the left-hand page. This gives the same two margins both the outer and inner margins. To maintain the proportion, the outer margin has a wider field. Classical layout pioneered by Jan Tschichold (1902-1974) a typographer from Germany is based on the size of the page with the proportion of 2: 3. Layout system is used almost in all areas related to visual design, you may have heard the word news layout, home layout, web layout etc.
The concept of HTTP Request and Response. To find out how the concept of Ajax you need to know how a web browser processes a request and receives a response from the web server. The standard used web browser at the moment is HTTP (HyperText Transfer Protocol). HTTP is used by the web browser to send requests from the website to the web server and then receive a response from the web server. HTTP requests work like emails, telling when a request is sent, containing headers that tell what the server should do and how to handle the request.
Once a request is received, the web server then determines what response will be provided. There are many existing request methods, but the most commonly used are GET and POST. Now that you have a shadow of how the request is sent to the web server and then the web server sends the response from the request to the web browser, it will be easy for you to understand how XMLHttpRequest works. Both are very similar, but XMLHttpRequest is operated behind the scenes and requires no page refresh.