Between Small and Large

A desktop browser accessing the website displays both the navigation bar and the block with the text on top of each other, as shown in Figure 6. However, if the user scales the browser window down to a width of less than 640 pixels, the browser switches to mobile mode because of the adaptive CSS layout, drops the navigation element and only displays the text block (Figure 7).

Figure 6: If the window is scaled up to more than 640 pixels, the navigation bar appears.

Figure 7: If the user drops the window width down to less than 640 pixels, the mobile version of the page appears on the desktop.

The 640 pixel-wide screen of, for example, an iPhone 5 also shows the mobile version without navigation aids because of the media query (Figure 8).

Figure 8: The mobile version shows on the iPhone 5 because of its 640-pixel page width.

The second media query in Listing 2, line 25, queries yet another display attribute. Using (orientation:landscape), it determines whether the display is in landscape mode.

If this is the case, the code from the sidebyside.css.tt file in Listing 4 is used; this shows the navigation and text elements next to one another, assigning 70 percent of space to the content and only 30 percent to navigation.

The value for the display variable of the navigation element is set to block in Listing  5. This overwrites the value of none, which possibly occurred in the previous media query, and restores the block value initially defined in the static CSS statement block.

The browser works its way through a list of media queries from the top down and overwrites the assigned values if the specified conditions are met. As a result, both blocks appear side by side, as shown in Figure 9.

Figure 9: In landscape mode, the content and navigation bar appear side by side.

Although the first media query only allows the text block without the navigation block, the landscape query overwrites all previous settings and lines up the blocks side by side at a 70:30 ratio.

Modular System

The tpage script, courtesy of the CPAN module Template::Toolkit, builds the page from the template items,

tpage --include_path templates templates/\
  test.html.tt >test.html

thus allowing a developer-friendly modular layout with full performance on the client and server sides; no assembly of page parts at run time is required because it already happens at page creation time.

Alternatively, you could instruct the browser to load only certain external CSS pages when a given media query returns a true value. However, each loading action costs precious time – the precompiled website is more efficient at run time.

If you want to test this quickly with a web server running locally, you can do it with a short script that uses the CPAN Mojolicious::Lite module, as shown in Listing 5. The script launches a fully functional web server on port 4080 of your localhost. Browsers accessing this will display the page differently depending on whether the browser window is wide, narrow, or in landscape format. To communicate with the Template Toolkit, the script requires the Mojolicious::Plugin::TtRenderer CPAN module.

If you want to delve deeper into this subject, I recommend the book Responsive Web Design with HTML 5 and CSS 3 [6]. It presents a number of practical application examples and explains techniques for dynamic page layout and adjusting image sizes for various mobile and desktop devices.