Wednesday, December 7, 2011

CSS performance

Recently we are looking at Javascript performance, and there are many good resources (like High Performance Javascript book), when looking at CSS, my first thought is all about selector. However, after reading slide, I realize that apart from selector/rendering performance, size/request numbers are still WPO fundamentals from CSS performance standpoint. Here are reading notes about "High Performance CSS" deck.

name - using abbreviation
shortcuts (zeror no unit, decimal beginning with zero need no zero, shorthand)
no final semicolon
minify (use a build script to run YUI compressor)
run ImageOptim against images
Gzip CSS

Number of requests
Concatenate your files
Use CSS sprites for buttons/hover status

Rendering/selector efficiency
from right to left (make key selector efficient)
avoid being too specific (avoid overqualified selectors)
universal selector selects every element, breaks inheritance
hardware acceleration - not suggested

Other tips
avoid CSS greater than 20KB
avoid CSS holds more than 4096 rules
border-radius, box-shadow and RGBA are all slow

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