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Understanding the Cascade

From: Dreamweaver CS3 Beyond the Basics

Video: Understanding the Cascade

Although it is a core CSS concept, many students are confused about the cascade of the cascading style sheets and how it works. In this movie we will explore the cascade and how we can take advantage of it to control our styles. Essentially the cascade states that the last style applied will win in the event of any conflict. So when a browser is interpreting your styles it looks at your external style sheets first then it renders those. It then looks for any embedded styles, styles that are going to exist in the Style tag in the Head of the document. That also applies to any styles that you have applied to your document using the Import rule. It's actually contained in the Style tag, so it would also override any external styles. Now lastly inline styles, the styles that you can apply directly to the tags themselves are applied and then they will override any external or embedded that they conflict with. This practice is discouraged against the accepted web standards of separating your structure from your presentation. So we really do it only in sort of a last ditch effort in order to get something to render. So back in Dreamweaver we are going to take a look at how we can take advantage of the cascade to really control specific elements on the page. The cascade also allows us to write modular styles. So we may have something that we want to occur globally throughout our entire site. So we will put that in an external style. But maybe there is something on just one specific page that we want to change. Well, that's perfect for an embedded style because we know it will override our external style sheets without affecting the rest of our site. So we are back in the rendering.htm file that we were working in the previous movie and if it's not visible, make sure your CSS styles is visible and I am just going to click over and switch to All mode so that I can see exactly what's going on in my file. Well, we are going to write a new CSS Rule and we do that by going down to the CSS Styles panel and there is the new CSS Rule icon at the very bottom of it, it looks like a little page with a plus symbol, I am going to click on that. That brings up our New CSS Rule dialog box. Now we are going to write an embedded style and since we are just going to do a very simple paragraph, from the Selector type I am going to choose Tag and I am going to write element selector and I will just type in p although it certainly could have also grabbed it from the pulldown menu. That gives me a list of available tags. Now at the very bottom of this you will notice that it expects me to define this in the external style sheet. Well, since I want to take advantage of the cascade and override paragraphs just in this file and not for my entire site, I will choose this document only. I am going to go ahead and click OK. That brings up our CSS Rule Definition dialog box. Well, I want to go ahead and change just a few things here. I am going to make my Size 1.2 ems, not pixels, because 1.2 pixels would be really small. And for Color I am just going to grab my color-picker and choose kind of a bright red. Now I am expecting this to restyle all my paragraphs because this is an embedded style and my external style sheet is right now currently defining what my paragraph should look like.

Understanding the Cascade

Although it is a core CSS concept, many students are confused about the cascade of the cascading style sheets and how it works. In this movie we will explore the cascade and how we can take advantage of it to control our styles. Essentially the cascade states that the last style applied will win in the event of any conflict. So when a browser is interpreting your styles it looks at your external style sheets first then it renders those. It then looks for any embedded styles, styles that are going to exist in the Style tag in the Head of the document. That also applies to any styles that you have applied to your document using the Import rule. It's actually contained in the Style tag, so it would also override any external styles. Now lastly inline styles, the styles that you can apply directly to the tags themselves are applied and then they will override any external or embedded that they conflict with. This practice is discouraged against the accepted web standards of separating your structure from your presentation. So we really do it only in sort of a last ditch effort in order to get something to render. So back in Dreamweaver we are going to take a look at how we can take advantage of the cascade to really control specific elements on the page. The cascade also allows us to write modular styles. So we may have something that we want to occur globally throughout our entire site. So we will put that in an external style. But maybe there is something on just one specific page that we want to change. Well, that's perfect for an embedded style because we know it will override our external style sheets without affecting the rest of our site. So we are back in the rendering.htm file that we were working in the previous movie and if it's not visible, make sure your CSS styles is visible and I am just going to click over and switch to All mode so that I can see exactly what's going on in my file. Well, we are going to write a new CSS Rule and we do that by going down to the CSS Styles panel and there is the new CSS Rule icon at the very bottom of it, it looks like a little page with a plus symbol, I am going to click on that. That brings up our New CSS Rule dialog box. Now we are going to write an embedded style and since we are just going to do a very simple paragraph, from the Selector type I am going to choose Tag and I am going to write element selector and I will just type in p although it certainly could have also grabbed it from the pulldown menu. That gives me a list of available tags. Now at the very bottom of this you will notice that it expects me to define this in the external style sheet. Well, since I want to take advantage of the cascade and override paragraphs just in this file and not for my entire site, I will choose this document only. I am going to go ahead and click OK. That brings up our CSS Rule Definition dialog box. Well, I want to go ahead and change just a few things here. I am going to make my Size 1.2 ems, not pixels, because 1.2 pixels would be really small. And for Color I am just going to grab my color-picker and choose kind of a bright red. Now I am expecting this to restyle all my paragraphs because this is an embedded style and my external style sheet is right now currently defining what my paragraph should look like.

So by the rule of the cascade I should override all my paragraphs. So I am going to click OK and see what happens. Well, they all got bigger, but only the paragraphs outside of the sidebar changed color. Now that tells us that there is more things than just the cascade that goes into rendering our style sheets. And we will explore those concepts in a couple of the later movies. Now I wanted to do one more rule here to understand the cascade. Currently you can see in our CSS Styles dialog box under All that we now have a Style tag and if I expand that I can see that I have the one paragraph rule inside that. Well, I am going to go ahead and create another rule and I am actually going to create another paragraph rule. That may seem kind of silly, but it's not uncommon to have multiple definitions of the same element and you are adding and taking away styling to it. So remember we are doing a Tag Selector and we are going to do it in this document only. So I will go ahead and click OK. Now for Size this time I am going to size it at 0.9 ems, so that's a smaller size, and this time I am going to add a property that we didn't had before. I am going to add Line height. So for Line height I am going to do 1.6 ems and make sure that you are not doing pixels, make sure you are doing ems, and that's all we are going to do in this rule. So we are resizing it and giving it a new line height. And once again I want to click OK. I can see that my document changes. Now we have got a lot of different rules now affecting our particular paragraphs. If I click inside the paragraph outside of the sidebar and I switch my CSS Styles View back to Current, now I can really take advantage of being able to see the cascade. You can see that the bottom rule is the one that's being applied last and then as I go back up my styles I can see all the different rules that are applying rendering to my paragraph. And when I click on my bottom one I can see that it's got the font-size and the line -height from that particular rule. When I click on the paragraph above it however notice that it's picking up color, but it's not picking up font-size and font-size has a strike through. When I hover over that I actually get a tool tip and Dreamweaver tells me why that property is not being rendered. So if you are expecting to see it at that size Dreamweaver would give you an idea as to why it's not being rendered and that's because of course the other paragraph rule is overriding it. So we get a nice overview of exactly what the cascade is doing when it renders out that final style. And if I clicked in one of the paragraphs in the sidebar I see that I have a whole another set of rules affecting it. So really understanding the cascade and understanding the order that the styles are going to be applied in is really a good point for beginning to understand how your style will be rendered within the browser. In our next movie we'll focus on another rendering concept, inheritance.

Show transcript

This video is part of

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Dreamweaver CS3 Beyond the Basics

102 video lessons · 38792 viewers

James Williamson
Author

 
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  1. 2m 3s
    1. Welcome
      1m 17s
    2. Using the exercise files
      46s
  2. 1h 23m
    1. Reviewing the Coding toolbar
      8m 42s
    2. Customizing the Coding toolbar
      9m 52s
    3. Taking advantage of Code Hinting
      7m 20s
    4. Using snippets and shortcuts
      11m 10s
    5. Using the Quick Tag Editor
      5m 18s
    6. Using Find and Replace
      9m 50s
    7. Regular expressions
      5m 39s
    8. Using Bridge with Dreamweaver CS3
      8m 28s
    9. Round-trip editing with Photoshop CS3
      3m 40s
    10. Leveraging image variables in Photoshop CS3
      7m 32s
    11. Integrating external variables into your workflow
      6m 16s
  3. 37m 26s
    1. Understanding the CSS Styles panel
      7m 59s
    2. Understanding the Cascade
      5m 50s
    3. Understanding Inheritance
      5m 8s
    4. Understanding Specificity
      7m 5s
    5. Managing CSS styles
      5m 4s
    6. Using Design-Time style sheets
      6m 20s
  4. 2h 19m
    1. Using the new CSS template pages
      5m 59s
    2. Understanding DIV tag structure and layout
      12m 0s
    3. Understanding the CSS box model
      10m 0s
    4. Using absolute and relative positioning
      8m 35s
    5. Understanding floating elements
      7m 9s
    6. Clearing floats
      7m 19s
    7. Using floats to control page layout
      3m 45s
    8. Building structure and assigning IDs
      10m 19s
    9. Applying basic styling to structured content
      11m 14s
    10. Positioning container elements
      11m 4s
    11. Enhancing layouts with background graphics
      11m 48s
    12. Creating faux columns with background graphics
      8m 55s
    13. Creating rounded corners with background graphics
      9m 17s
    14. Building navigation with CSS
      16m 57s
    15. Using Dreamweaver's Browser Check feature
      5m 31s
  5. 53m 22s
    1. Creating properly structured forms
      6m 30s
    2. Creating accessible forms
      6m 41s
    3. Using CSS to lay out form structure
      7m 40s
    4. Creating vertical columns for form elements
      7m 48s
    5. Adding user feedback
      5m 52s
    6. Applying advanced styling to forms
      8m 11s
    7. Client-side form validation
      4m 17s
    8. Validating forms with the Spry Validation tools
      6m 23s
  6. 1h 20m
    1. Understanding the Spry framework
      3m 43s
    2. Defining a data source for use in Spry
      3m 56s
    3. Creating a Spry table
      8m 8s
    4. Using the Spry widgets
      8m 11s
    5. Connecting various data sets
      4m 50s
    6. Understanding Spry widget structures
      7m 1s
    7. Applying custom styles to Spry widgets
      6m 24s
    8. Applying additional custom styles to Spry widgets
      8m 46s
    9. Controlling Spry widget behaviors with JavaScript
      6m 0s
    10. Controlling Spry widget animations with JavaScript
      9m 31s
    11. Creating effects with Spry behaviors
      4m 42s
    12. Hand-coding Spry
      9m 11s
  7. 1h 11m
    1. Creating a base template
      8m 6s
    2. Creating editable attributes
      6m 26s
    3. Creating a new page from a template
      7m 42s
    4. Applying a template to an existing page
      4m 36s
    5. Creating nested templates
      5m 24s
    6. Using repeating regions
      6m 34s
    7. Creating editable and non-editable optional regions
      6m 0s
    8. Using template parameters
      7m 26s
    9. Using template expressions
      9m 59s
    10. Using conditional template expressions
      8m 54s
  8. 54m 40s
    1. Examining XML structure
      2m 44s
    2. Creating an XML document
      9m 9s
    3. Using the CDATA structure
      5m 7s
    4. Creating an XSLT file
      4m 33s
    5. Binding data from an XML to an XSLT document
      5m 6s
    6. Inserting repeating regions into an XSL document
      5m 16s
    7. Creating a client-side XSL transformation
      2m 52s
    8. Styling a remote RSS feed
      7m 29s
    9. Creating a server-side XSL transformation
      5m 31s
    10. Writing XSL expressions
      6m 53s
  9. 1h 2m
    1. Overview of building dynamic websites
      1m 35s
    2. Installing PHP, MySQL, and Apache on Mac
      3m 22s
    3. Installing PHP, MySQL, and Apache on Windows
      3m 54s
    4. Creating a MySQL database
      3m 16s
    5. Defining a testing server and database bindings
      6m 14s
    6. Creating a database recordset
      4m 35s
    7. Adding dynamic content to the page
      5m 14s
    8. Creating repeating regions of dynamic content
      7m 6s
    9. Filtering database records
      7m 39s
    10. Using the Live Preview
      10m 22s
    11. Passing URL parameters
      4m 23s
    12. Dynamically generating links
      5m 18s
  10. 57m 9s
    1. Understanding behaviors
      5m 16s
    2. Installing additional behaviors
      3m 39s
    3. Planning to create a custom behavior
      3m 42s
    4. Examining existing behaviors
      5m 32s
    5. Building a behavior function
      7m 23s
    6. Creating an Action file
      6m 48s
    7. Enabling behavior functions
      9m 1s
    8. Initializing the user interface for a behavior
      3m 9s
    9. Loading behaviors in Dreamweaver
      6m 47s
    10. Testing and debugging behaviors
      5m 52s
  11. 27m 12s
    1. Running reports
      7m 41s
    2. Checking and validating links
      3m 40s
    3. Using cloaking
      5m 42s
    4. Using Check In/Check Out
      4m 3s
    5. Using Design Notes
      6m 6s
  12. 20s
    1. Goodbye
      20s

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