Fixed-width layouts are very common as they give the developer more control over layout and positioning. Once set the width of the design to be 720 pixels wide, it will always be 720 pixels. If you want a branding image spanning the top of the design, you know it needs to be 720 pixels wide to fit. Knowing the exact width of each element allows lay them out precisely and knowing where everything will be. This predictability makes fixed-width layout by far the most common layout method around.
However, fixed-width designs have their downsides. First, they are fixed; they are always the same size no matter what the window size. As such, they don’t make good use of the available space. On large screen resolutions, designs created for 800 x 600 can appear tiny and lost in the middle of the screen. Conversely, a design created for a 1024 x760 screen will cause horizontal scrolling on smaller screen resolutions. With an increasingly diverse range of screen sizes to contend with, fixed-width design is starting to feel like a poor compromise. Another issue with fixed-width design revolves around line lengths and text legibility. Fixed-width layouts usually work well with the browser default text size. Only have to increase the text size a couple of steps before sidebars start running out of space and the line lengths get too short to comfortably read.
To work around these issues, you could choose to use liquid or elastic layout instead of fixed-width layout.
With liquid layouts, dimensions are set using percentages instead of pixels. This allows liquid layouts to scale in relation to the browser window. As the browser window gets bigger, the columns get wider. As the window gets smaller, the columns will reduce in width. Liquid layouts make for very efficient use of space. However, liquid layouts are not without their own problems. At small window widths, line lengths can get incredibly narrow and difficult to read. This is especially true in multicolumn layouts. As such, it may be worth adding a min-width in pixels to prevent the layout from becoming too narrow.
Conversely, if the design spans the entire width of the browser window, line lengths can become long and difficult to read. There are a couple of things that helps to avoid this problem. First, rather than spanning the whole width, make the wrapper span just a percentage-say, 85 percent. Consider setting the padding and margin as percentages as well. That way, the padding and margin will increase in width in relation to the window size, stopping the columns from getting too wide, too quickly. Lastly, for very severe cases, choose to set the maximum width of the wrapper in pixels to prevent the content from getting ridiculously wide on oversized monitors.
You can use these techniques to turn the previous fixed-width, three-column layout into a fluid, three-column layout. Start by setting the width of the wrapper as a percentage of the overall width of the window. Set the width of the navigation and content areas as a percentage of the wrapper width. After a bit of trial and error, setting the navigation area to be 23 percent and the content area to 75 percent produced nice results. This leaves a 2-percent virtual gutter between the navigation and the wrapper to deal with any rounding errors and width irregularities that may occur.
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