Page layout

Part of the user interface design is affected by the quality of the page layout. For example, a designer may consider whether the site's page layout should remain consistent on different pages when designing the layout. Page pixel width may also be considered vital for aligning objects in the layout design. The most popular fixed-width websites generally have the same set width to match the current most popular browser window, at the current most popular screen resolution, on the current most popular monitor size. Most pages are also center-aligned for concerns of aesthetics on larger screens.

Fluid layouts (sometimes called responsive design) increased in popularity around 2000 as an alternative to HTML-table-based layouts and grid-based design in both page layout design principle and in coding technique, but were very slow to be adopted. This was due to considerations of screen reading devices and varying windows sizes which designers have no control over. Accordingly, a design may be broken down into units (sidebars, content blocks, embedded advertising areas, navigation areas) that are sent to the browser and which will be fitted into the display window by the browser, as best it can. As the browser does recognize the details of the reader's screen (window size, font size relative to window etc.) the browser can make user-specific layout adjustments to fluid layouts, but not fixed-width layouts. Although such a display may often change the relative position of major content units, sidebars may be displaced below body text rather than to the side of it. This is a more flexible display than a hard-coded grid-based layout that doesn't fit the device window. In particular, the relative position of content blocks may change while leaving the content within the block unaffected. This also minimizes the user's need to horizontally scroll the page.

Responsive web design is a newer approach, based on CSS3, and a deeper level of per-device specification within the page's style sheet through an enhanced use of the CSS. In March 2018 Google announced they would be rolling out mobile-first indexing.Sites using responsive design are well placed to ensure they meet this new approach.

Introduction to the box model

The CSS box model describes the box rendering object. This object is characterized in particular by three groups of properties: margin, padding, and border, described below.

For information on the layout of boxes, please consult the section on the visual flow model.

The page box is a special kind of box which is described in detail on the section on paged media.