CSS and image optimization
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The document discusses various techniques for optimizing CSS and images to improve page load performance. It recommends reducing CSS file sizes through minification and reusable rules, minimizing HTTP requests by inlining critical CSS and using sprites, and optimizing image file sizes by converting GIFs to PNGs and running JPEG and PNG files through optimization tools. Analyzing the top 1000 sites revealed opportunities to reduce file sizes through these techniques, saving over 20% for CSS and over 10% for images on average.
![MHTML - multi parts
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![Gradients
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background-image: -webkit-gradient(linear, left top, left bottom,
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CSS and image optimization
- 1. CSS and Image Optimization Stoyan Stefanov, @stoyanstefanov May 12, 2010 Web Optimization Summit
- 2. Agenda 1. Reducing CSS file sizes 2. Rendering 3. Reducing HTTP requests 4. Optimizing image file sizes
- 3. Reducing CSS file sizes
- 4. CSS recipe for disaster #sidebar #menu ul li.blogroll { color: green !important; font-weight: bold; }
- 5. CSS recipe for disaster #sidebar #menu ul li.blogroll { color: green !important; font-weight: bold; } Long selectors
- 6. CSS recipe for disaster #sidebar #menu ul li.blogroll { color: green !important; font-weight: bold; } C-style indented declarations
- 7. CSS recipe for disaster #sidebar #menu ul li.blogroll { color: green !important; font-weight: bold; } What? Not unique enough?
- 8. CSS recipe for disaster #sidebar #menu ul li.blogroll { color: green !important; font-weight: bold; } One is probably enough
- 9. CSS recipe for disaster #sidebar #menu ul li.blogroll { color: green !important; font-weight: bold; } Lame
- 10. Crockford on CSS: “Long, fragile lists of self-contradictory rules”
- 11. So? #sidebar #menu ul li.blogroll { color: green !important; font-weight: bold; } Legend: • easy stuff • tough stuff
- 12. So? Make the tough stuff easy
- 13. Reusable CSS .linklist {color: green; ...} /* widgets */ .module {...} .gallery {...} /* utilities */ .clearfix {...}; .flip {...}
- 14. Mixin pattern <ul class="module linklist"> …
- 15. Reusable CSS 1. Strong foundation: reset, grids 2. Library styles: .class not #id
- 16. Object-Oriented CSS • Nicole Sullivan • oocss.org
- 17. Minifying CSS • Strip white space, comments • Some micro-optimizations • ~30% savings • can’t rename • YUICompressor, CSSTidy • Inline code too! http://tools.w3clubs.com/cssmin/
- 18. Browser-specific CSS • IE6,7 vs. others • -webkit-, -moz-, -o- • -ms-, _, *, zoom • automated • savings? 3-5%, mileage vary http://phpied.com/files/css-parse/css-strip.html
- 20. Filters • AlphaImageLoader is bad • Verdict is out on the others
- 21. Expressions • Executed too often • Avoid • JavaScript or self-rewrite
- 22. Behaviors • Be careful with the shims • ie-css3.htc, pngfix.htc,…
- 23. Scrollbars trick • Prevent a reflow when you expect a long page body {overflow-y: scroll;}
- 25. CSS blocks rendering • The worst component type • Place way at the top • Inline all @media print, etc http://www.phpied.com/delay-loading-your-print-css/ http://www.phpied.com/rendering-styles/
- 26. Same domain • If you split across domains, keep CSS on the same domain as HTML
- 27. Inline CSS • Google search • Bing.com: inline + postload
- 28. Inline + postload • First visit: 1. Inline 2. Lazy-load the external file 3. Write a cookie
- 29. Inline + postload • Later visits: 1. Read cookie 2. Refer to the external file
- 30. Web Fonts • Don’t go overboard! • Subset • Gzip! http://snook.ca/archives/html_and_css/ screencast-converting-ttf2eot
- 31. Fewer HTTP requests • Inline images: in CSS sprites with data: URI scheme http://csssprites.com http://spriteme.org
- 32. Fewer HTTP requests • data: URI scheme $ php ‐r "echo base64_encode(file_get_contents('my.png'));” iVBORw0KGgoAAAANSUhEUgAAAAQAAAADCAIAAAA7ljmRAAAAGElEQVQIW2P 4DwcMDAxAfBvMAhEQMYgcACEHG8ELxtbPAAAAAElFTkSuQmCC
- 33. Fewer HTTP requests • data: URI scheme background‐image: url("data:image/ png;base64,iVBORw0KG...");
- 34. Fewer HTTP requests • data: URI scheme <img src="data:image/png;base64,iVBOR..." />
- 37. Fewer HTTP requests • data: URI scheme • works in IE!...
- 38. Fewer HTTP requests • data: URI scheme • works in IE8!
- 39. Fewer HTTP requests • data: URI scheme • MHTML for IE < 8
- 40. MHTML • MIME HTML • Works in IE 6,7 • Indeed it actually absolutely does work in IE7/Vista too
- 41. MHTML - one part Content-Location: myimage Content-Transfer-Encoding: base64 iVBORw0KGgoAAAANSU....U5ErkJggg==
- 42. MHTML - multi parts Content-Type: multipart/related; boundary="MYSEPARATOR" --MYSEPARATOR [here comes part one] The double- --MYSEPARATOR dash of doom [here's part two] --MYSEPARATOR--
- 43. MHTML – all together /* Content-Type: multipart/related; boundary="MYSEPARATOR" --MYSEPARATOR Content-Location: myimage Content-Transfer-Encoding: base64 iVBORw0KGgoAAAANSUhEUgAAABgAAAAYCAMAAADXqc3KAAAD....U5ErkJggg== --MYSEPARATOR Content-Location: another Content-Transfer-Encoding: base64 iVBORw0KGgoAAAANSUhEUgAAABgAAAAYCAMAAADXqc3KAAAA....U5ErkJggg== --MYSEPARATOR-- */ .myclass { background-image:url(mhtml:http://example.org/styles.css!myimage); } .myotherclass { background-image:url(mhtml:http://example.org/styles.css!another); }
- 44. MHTML + data URI • drawback: repeats the same encoded image • solution: browser-specific CSS • or… an ingenious hack
- 45. MHTML + data URI • image header + css + data /9j/4AA0;background-image:url(data:image/jpeg;base64;00,/9j/4AA0 Reality: IE: Others: http://habrahabr.ru/blogs/webdev/90761/
- 46. No-image UI • a.k.a. CSS3
- 47. Rounded corners .module { -moz-border-radius: 9px; -webkit-border-radius: 9px; border-radius: 9px; }
- 48. Rounded corners All vs. IE
- 49. Gradients .hd { background-image: -moz-linear-gradient(top, #641d1c, #f00); background-image: -webkit-gradient(linear, left top, left bottom, from(#641d1c), to(#f00)); filter: [...].gradient(startColorstr=#ff641d1c,endColorstr=#ffff0000); -ms-filter: "[...].gradient(startColorstr=#ff641d1c,endColorstr=#ffff0000)"; }
- 50. No-image UI • rounded corners • gradients • glows, shadows • rgba http://www.phpied.com/ css-performance-ui-with-fewer-images/ http://css3please.com
- 51. Multi-purpose “mask” images • one image on top of different solid colors • for themes, social profiles…
- 52. 1px wide “mask” • Top: somewhat transparent • Bottom: Fully transparent
- 54. Gradient mask • the data URI smaller that all the CSS –moz, -webkit, filter...
- 55. A glossy mask
- 56. Optimizing image file sizes
- 57. Rule #1: No GIFs $ optipng *.gif
- 58. PNG-8 • Palette image (like GIF) • 256 colors (like GIF) • Smaller than GIF (GIF++) • Alpha transparency (GIF++)
- 60. PNGSlim OptiPNG DeflOpt PNGOut PNGOptimizer PNGCrush AdvPNG PNGRewrite
- 61. JPEG • The format for photos • Run through JPEGTran
- 62. Study of the images on the top 1000 sites Q: How many GIFs are out there? Q: What if we make them PNG? Q: Are PNGs optimized? Q: Are JPEGs optimized?
- 63. Top 1000 – how? • URLs from Alexa top sites • open Fiddler • php script that opens/closes Explorer with each URL • enjoy! • Export images from Fiddler
- 64. Top 1000 – GIF vs. PNG? Animated GIF 3% PNG 24% GIF 73%
- 65. Top 1000 – GIF vs. PNG vs. JPG? GIF 40% JPEG 46% PNG Animated GIF 13% 1%
- 66. Top 1000 – GIF to PNG $ optipng *.gif $ pngoptimizercl – file:"*.png” (1 min/1000 files) 23.79% savings
- 68. Top 1000 – Optimizing PNG $ pngoptimizercl – file:"*.png" 16.90% savings
- 69. Top 1000 – Optimizing JPG $ jpegtran –copy none -optimize 13.08% savings
- 70. Take-home 1. Think reusable CSS 2. Reduce HTTP requests: - sprites, data URIs - CSS3, reusable images 3. Smush all images