Layout

Key Concepts in Positioning El ements

Building Blocks

CSS treats each HTML element as if it is in its own box. This box will either be a block-level box or an inline box. Block-level boxes start on a new line and act as the main building blocks of any layout, while inline boxes flow between surrounding text. You can control how much space each box takes up by setting the width of the boxes (and sometimes the height, too). To separate boxes, you can use borders, margins, padding, and background colors.

Containing Elements

If one block-level element sits inside another block-level element then the outer box is known as the containing or parent element. It is common to group a number of elements together inside a [< div >] (or other block-level) element. For example, you might group together all of the elements that form the header of a site (such as the logo and the main navigation). The [< div >] element that contains this group of elements is then referred to as the containing element.

Controll ing the Position of El ements

CSS has the following positioning schemes that allow you to control the layout of a page: normal flow, relative positioning, and absolute positioning. You specify the positioning scheme using the position property in CSS. You can also float elements using the float property. To indicate where a box should be positioned, you may also need to use box offset properties to tell the browser how far from the top or bottom and left or right it should be placed. (You will meet these when we introduce the positioning schemes on the following pages.)

Screen Sizes

Different visitors to your site will have different sized screens that show different amounts of information, so your design needs to be able to work on a range of different sized screens.

Screen Resolution

Resolution refers to the number of dots a screen shows per inch. Some devices have a higher resolution than desktop computers and most operating systems allow users to adjust the resolution of their screens.

Page Sizes

Because screen sizes and display resolutions vary so much, web designers often try to create pages of around 960-1000 pixels wide (since most users will be able to see designs this wide on their screens).

Fixed Width Layouts

Fixed width layout designs do not change size as the user increases or decreases the size of their browser window. Measurements tend to be given in pixels.

Liquid Layouts

Liquid layout designs stretch and contract as the user increases or decreases the size of their browser window. They tend to use percentages.

Layout Grids

Composition in any visual art (such as design, painting, or photography) is the placement or arrangement of visual elements — how they are organized on a page. Many designers use a grid structure to help them position items on a page, and the same is true for web designers.