This document discusses performance considerations for customizing Blackboard themes using CSS. It introduces CSS and provides best practices like avoiding unused selectors, overqualified selectors, and the :hover pseudo-selector. Images should use appropriate formats like JPEG and PNG, and be optimized. CSS and images should be minified for faster loading. Tools like Firebug and PageSpeed can analyze performance and identify issues.

1. Performance Considerations for
Custom Theme Development
Kevin Weisser
Noriaki Tatsumi

2. Overview
• Introduction to Themes
• Blackboard Customization Approach
• Introduction to CSS
• CSS Performance Considerations
• Image Performance Considerations
• Front-end Analysis Tools

3. Blackboard Custom Themes

4. Blackboard Custom Themes

5. Blackboard Custom Themes
• Blackboard 9.x contains a flexible user interface
which can be easily branded to have the look
and feel of your institution
• This can be accomplished by changing any of
the following:
– Themes/Color Palettes
– Images
– Customizing Login Page

6. Blackboard’s Recommended
Customization Approach
1. Access Learn as System Administrator
2. Navigate to System Admin tab
3. Click on Brands and Themes
4. Click on Theme and Palette Catalog
5. Click icon beside BbLearn Theme
6. Download the theme and save it to your
desktop

7. Blackboard’s Recommended
Customization Approach
7. From Theme and Palette Catalog, select Create
Theme
8. Provide the required fields (Theme Name and
Reference Name) and click Browse My Computer
9. Select the recently downloaded theme
10. Click Submit
11. Open the file on the application server (Bb root-
>content->vii->BBLEARN->branding->themes-
>Your Theme Folder) in your favorite editor and
proceed to make your changes

8. Blackboard’s Recommended
Customization Approach Cont.

9. Performance Stories From the Field
• Customized login page loads slowly
– Mitigated by limiting the requests to those used by
the browser
• Drag and drop functionality appears choppy
– Mitigated by cleaning up poor performing CSS
selectors
• Pages load slowly in areas with limited
connectivity
– Mitigated by leveraging browser cache and
ensuring that requests were compressed/minified

10. Introduction to CSS
• Imagine the following block:
...
ul#summer-drinks li {
font-weight: normal;
font-size: 12px;
color: black;
}
…
<ul id="summer-drinks">
<li>Whiskey and Ginger Ale</li>
<li>Wheat Beer</li>
<li>Mint Julip</li>
</ul>
…

11. Introduction to CSS
• You want to designate a favorite:
…
ul#summer-drinks li {
font-weight: normal;
font-size: 12px;
color: black;
}
.favorite {
color: red;
font-weight: bold;
}
…
<ul id="summer-drinks“>
<li class=“favorite”>Whiskey and Ginger Ale</li>
<li>Wheat Beer</li>
<li>Mint Julip</li>
</ul>

12. Introduction to CSS
Selector Specificity
* 0,0,0,0
li 0,0,0,1
ul li 0,0,0,2
ul ol li.red 0,0,1,3
li.red.level 0,0,2,1
#x34y 0,1,0,0
style=“display:none” 1,0,0,0

13. Introduction to CSS
• Higher specificity selectors are applied
• Last style declared is applied when a tie exists
• !important overrides the specificity

14. Quantifying Impact

15. CSS Performance Considerations
• Anti-patterns
– Unused Selectors
– Universal Selectors
– Over Qualified Selectors
– :hover Pseudo Selector
– Descendant Selectors
– @import Usage
• Optimization
– Minification

16. Unused Selectors
• What are unused selectors?
– Declared selectors which are not applied to any
element of the DOM
• How does this impact performance?
– CSS is blocking
– More Styles = Larger Files = Longer download
times
– More Styles = More Parsing
– More Styles = More Evaluations

17. Unused Selectors
• Mitigation techniques
– Split external CSS into smaller files grouped by
related functionality/styles
– When adding styles:
• Be aware of already defined styles
• Be aware of selector specificity
• Be aware of which attributes are available various
DOM elements

18. Universal Selector
• What is a universal selector?
– Universal selectors are denoted by the ‘*’ symbol
• Example: .itemGallery *{zoom:1;}
• How does this impact performance?
– Right to left evaluation
– Reflow in interactive pages
• Mitigation techniques
– Be specific

19. Universal Selector

20. Universal Selector

21. Over Qualified Selectors
• What is an over qualified selector?
– ID selectors denoted by ‘#’ that has a preceding
element tag
• Example: div#lightboxContent h2{position:relative};
– Class selectors denoted by ‘.’ that has a preceding
element tag
• Example: div.stopped p img{background:#fff -180px;}

22. Over Qualified Selectors
• How does this impact performance
– One more comparison is required during evaluation
• Mitigation techniques
– Don’t specify the element before the ID/Class
selector
– IDs should be unique
– Classes can be unique

23. :hover Psuedo Selector
• What is the :hover pseudo selector?
– Elements that specify a different style when the
mouse hovers over the element element
• Example:
– tr.S {background-color:#000000}
– tr.S:hover {background-color:#FFFFFF}
• How does this impact performance?
– IE degradation on non-anchor elements
– IE9 may correct this problem

24. :hover Psuedo Selector
• Mitigation techniques
<style type="text/css">
tr.S {background-color:#000000}
tr.S:hover {background-color:#FFFFFF}
</style>
<table>
<tr class="S">
<td>foo bar</td>
</tr>
</table>
<table>
<tr style="background-color:#FFFFFF"
onmouseover="this.style.backgroundColor='#000000'"
onmouseout="this.style.backgroundColor='#FFFFFF'">
<td>foo bar</td>
</tr>
</table>

25. Descendant Selector
• What are descendant selectors?
– Descendant selectors filter based criteria
• Example: treehead treerow treecell {…}
• How does this impact performance?
– More evaluations

26. Descendant Selector
• Mitigation techniques
– Use of child selectors prevent DOM traversal
• treehead > treerow > treecell {…}
– Class selector is preferred
• .treecell-header {…}
– Use caution this approach can reduce reusability

27. @import Usage
• What does @import do?
– Allows stylesheets to include other stylesheets
• How does this impact performance?
– Set number of connections available to request
resources
– Eliminates parallelism
• Mitigation techniques
– <link> tags alllow for parallel CSS download

28. CSS Minification
• Process which removes comments, return
characters, and unnecessary white space
• Sacrifices readability for smaller file sizes
• Free tools available (ex. YUICompressor)
• Themes uploaded from the System Admin tab
are immediately compressed

29. CSS Minification

30. Image Performance Considerations
• Anti-patterns
– Inappropriate image format
– Unreachable images
– Unused Images

31. Inappropriate Image Format:
JPEG
• Recommended for realistic pictures with smooth
gradients and color tones
• Not lossless
• Sacrifice compression for resolution
• JPEGTran optimization

32. Inappropriate Image Format:
PNG and GIF
• PNG and GIF should be used for solid color images
(charts or logos)
• Use PNG over GIF unless
– Image contains animation
– Image is extremely small (a few hundred bytes),
because GIF tends to be smaller than PNG
• PNG is superior because
– Copyright free
– More efficient compression
– Stores all bit depths
• OptiPNG, PNGCrush for optimization

33. Unreachable Images
• Make sure path to image is correct
• 404 status on any request is a wasted request
– Request may be blocking
– Reduces parallelism
• Verify all images are reachable via browser
profile tools, such as Firebug

34. Unused Images
• Request to unused images creates unnecessary
delays
• Longer download times
• Reduced parallelism

35. Front End Analysis Tools
• Firebug (http://getfirebug.com/)
– Inspect HTML and modify style/layout in real-time
– Debug JavaScript
– Analyze network usage and performance
• PageSpeed (http://code.google.com/speed/page-speed/)
– Optimize with Web performance best practices
– Rules of particular interest
• Avoid bad requests
• Avoid CSS @import
• Combine external CSS
• Minify CSS
• Optimize Images
• Use efficient CSS Selectors

36. Questions & Answers

37. Please provide feedback for this session by emailing
DevConFeedback@blackboard.com.
The title of this session is:
Performance Considerations for Custom Theme (CSS)
Development