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CSS – Responsive design details

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Using Hardware Pixels to Design a Responsive Website
When designing a responsive website, we suggest you use 3 different sizes: 1) For a regular desktop, use the width of 1200 pixels, 2) for an iPad the format is 768 x 1024 pixels and 3) for an iPhone 5 the format is 320 x 568 pixels. Why these 3 formats? Simple, because a 1920 x 1080 is the most common HD desktop size, the regular size iPad is a common tablet size and the iPhone 5 is the smallest size you should be designing for. But in fact, you are actually designing for 5 formats when you consider that a mobile device can be used either vertically or horizontally.


– from:

Absolute Lengths

– Avoid these as they lack adjustment with changing screen size

Unit Description
cm centimeters
mm millimeters
in inches (1in = 96px = 2.54cm)
px * pixels (1px = 1/96th of 1in)
pt points (1pt = 1/72 of 1in)
pc picas (1pc = 12 pt)


Relative Lengths

Unit Description
em Relative to the font-size of the element (2em means 2 times the size of the current font)
ex Relative to the x-height of the current font (rarely used)
ch Relative to width of the “0” (zero)
rem Relative to font-size of the root element
vw Relative to 1% of the width of the viewport*
vh Relative to 1% of the height of the viewport*
vmin Relative to 1% of viewport’s* smaller dimension
vmax Relative to 1% of viewport’s* larger dimension
% Relative to the parent element

– Relative units (as listed above) are the most useful in responsive design. ‘rem’ in particular is popular as it is relative to the root font size. A popular approach is to set the font size for the ‘html’ tag to 62.5% (ie

 html{ font-size:62.5%; }

) which changes the default of 16px to 10px and this simplifies any ratios where rem is to be used (ie font-size of 16px would be achieved by using:

font-size: 1.6rem;


Media Query Syntax


@media not|only mediatype and (expressions) {

You can also have different stylesheets for different media:

<link rel=”stylesheet” media=”mediatype and|not|only (expressions)”

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