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CSS: Core Concepts

ID selectors


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CSS: Core Concepts

with James Williamson

Video: ID selectors

ID selectors work in much the same way as class selectors, in that they allow us to target any element on the page with a specific ID attribute. Now there are a few slight differences between the selectors that you need to be aware of, so let's take a closer look at ID selectors. And you can do that by opening up the id-selector.htm, which you can find in the 02_04 folder in the exercise files Chapter_02 folder. So essentially, looking at this page, the structure is pretty much exactly the same.
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  1. 4m 57s
    1. Welcome
      55s
    2. Using the exercise files
      4m 2s
  2. 1h 7m
    1. Exploring default styling
      4m 56s
    2. CSS authoring tools
      2m 29s
    3. CSS syntax
      4m 45s
    4. Writing a selector
      4m 10s
    5. Setting properties
      8m 40s
    6. Common units of measurement
      7m 47s
    7. Inline styles
      5m 1s
    8. Embedded styles
      5m 19s
    9. Using external style sheets
      10m 34s
    10. Checking for browser support
      8m 48s
    11. Dealing with browser inconsistencies
      5m 30s
  3. 2h 15m
    1. Structuring HTML correctly
      2m 51s
    2. Element selectors
      4m 52s
    3. Class selectors
      6m 4s
    4. ID selectors
      3m 27s
    5. Using classes and IDs
      10m 7s
    6. Element-specific selectors
      4m 35s
    7. The universal selector
      5m 42s
    8. Grouping selectors
      4m 49s
    9. Descendent selectors
      7m 32s
    10. Child selectors
      5m 7s
    11. Adjacent selectors
      5m 30s
    12. Attribute selectors
      12m 43s
    13. Pseudo-class selectors
      3m 54s
    14. Dynamic pseudo-class selectors
      8m 29s
    15. Structural pseudo-class selectors
      6m 45s
    16. Nth-child selectors
      13m 10s
    17. Pseudo-element selectors
      12m 40s
    18. Targeting page content: Lab
      8m 56s
    19. Targeting page content: Solution
      7m 59s
  4. 42m 39s
    1. What happens when styles conflict?
      4m 0s
    2. Understanding the cascade
      5m 47s
    3. Using inheritance
      6m 11s
    4. Selector specificity
      6m 55s
    5. The !important declaration
      4m 5s
    6. Reducing conflicts through planning
      3m 33s
    7. Resolving conflicts: Lab
      6m 45s
    8. Resolving conflicts: Solution
      5m 23s
  5. 1h 47m
    1. Setting a font family
      7m 10s
    2. Using @font-face
      9m 18s
    3. Setting font size
      7m 35s
    4. Font style and font weight
      6m 52s
    5. Transforming text
      3m 58s
    6. Using text variants
      2m 49s
    7. Text decoration options
      4m 26s
    8. Setting text color
      3m 2s
    9. Writing font shorthand notation
      8m 49s
    10. Controlling text alignment
      6m 33s
    11. Letter and word spacing
      9m 11s
    12. Indenting text
      4m 30s
    13. Adjusting paragraph line height
      10m 30s
    14. Controlling the space between elements
      6m 41s
    15. Basic text formatting: Lab
      8m 45s
    16. Basic text formatting: Solution
      7m 14s
  6. 2h 1m
    1. Understanding the box model
      16m 53s
    2. Controlling element spacing
      14m 29s
    3. Controlling interior spacing
      10m 49s
    4. Margin and padding shorthand notation
      6m 27s
    5. Adding borders
      8m 57s
    6. Defining element size
      10m 7s
    7. Creating rounded corners
      6m 58s
    8. Background properties
      2m 51s
    9. Using background images
      5m 10s
    10. Controlling image positioning
      10m 25s
    11. Using multiple backgrounds
      7m 5s
    12. Background shorthand notation
      5m 25s
    13. Styling container elements: Lab
      7m 55s
    14. Styling container elements: Solution
      8m 17s
  7. 47m 51s
    1. Color keyword definitions
      5m 4s
    2. Understanding hexadecimal notation
      6m 5s
    3. Using RGB values
      4m 58s
    4. Using HSL values
      5m 17s
    5. Working with opacity
      2m 23s
    6. Using RGBa and HSLa
      3m 8s
    7. Styling drop shadows
      5m 38s
    8. CSS gradients
      6m 32s
    9. Working with color: Lab
      4m 26s
    10. Working with color: Solution
      4m 20s
  8. 1m 58s
    1. Additional resources
      1m 58s

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CSS: Core Concepts
8h 49m Beginner Nov 22, 2011

Viewers: in countries Watching now:

In this hands-on course, James Williamson demonstrates the concepts that form the foundation of Cascading Style Sheets (CSS), including styling text, adding margins and padding, and controlling how images display. The course also explores the tools needed to work with CSS, the differences between embedded and external styles, how to use selectors to target elements, and what to do when styles conflict.

Topics include:
  • Exploring default styling
  • Writing a selector
  • Setting properties
  • Working with common units of measurement, including ems and pixels
  • Structuring HTML correctly
  • Understanding the cascade and inheritance
  • Setting a font family, font size, text color, and more
  • Understanding the box model
  • Styling container elements
  • Working with RGB vs. HSL values
  • Styling drop shadows
Subject:
Web
Software:
CSS
Author:
James Williamson

ID selectors

ID selectors work in much the same way as class selectors, in that they allow us to target any element on the page with a specific ID attribute. Now there are a few slight differences between the selectors that you need to be aware of, so let's take a closer look at ID selectors. And you can do that by opening up the id-selector.htm, which you can find in the 02_04 folder in the exercise files Chapter_02 folder. So essentially, looking at this page, the structure is pretty much exactly the same.

Now we have stripped off any those classes that we had on our earlier elements. We just want to give some IDs. Now IDs, again, are just like classes in terms of the fact that they are an attribute. So if I go to our first aside right here, for example, and I type in id=, I can just go ahead and give it any value that I want. In this case, I am going to call it aside1. So we are using the same names that we used before, only this time instead of a class attribute, it's an ID attribute. The same thing for the second aside, I am going to give it an id="aside2." So, so far, not much difference; I am just using the ID attribute instead of a class attribute. But as you write the selector for them, the syntax is a tad bit different.

So when I go back up to this little area where I am going to add my styles right here on line 37, to write an ID selector, you first start with the pound symbol, also known as the octothorpe. And then I can go ahead and follow that with the name of the attribute that I want to use, in this case aside1. In this case, I am going to go ahead and just apply a different background to each one of these. I am just going to do background and I want to say beige. That's a good color. Now Aptana is trying--and you may have noticed this in an earlier movie too-- it's trying to save me from myself, essentially throwing up a little code error here.

And if I hover over that, it will even try to tell me that hey, this color value is not a defined property. Well, it is. In the Color Level 3 specification it certainly is. It is also part of the SVG specification, and so because of that, it's been supported by browsers for years and years and years, so you can use it without fear. That's nice of Aptana to tell me that, but not a big deal. Right now, on the next line I am going to do the same thing, #aside2, and again here I am going to do background, and we will do tan. So we get beige and tan, two very exciting colors. So again, notice that the pound symbol identifies this is an ID and if we go down to our page, we can find the associated attribute. And if I save this and preview this in one of my browsers, I can see that I have tan and brown backgrounds for my asides respectively.

Okay so what else is different in terms of classes and IDs? Well, for IDs I can only use this aside1 value one time per page, so IDs must be unique. So before where we were able to use the blueHeading class multiple times, here I could use this particular ID only once. So you can have multiple IDs per page, just not the same IDs, so it has to be unique. Now in terms of CSS, that means that in the event that a class and ID selector conflict with each other, the ID selector's styling will be used in favor of the class because it's more specific.

At first glance, using class and ID selectors might seem simple, but there's a fair amount of thought that should go into using them before you actually execute them in your code, so in our next movie, I am going to go a little deeper into the strategies behind using both of those selector types.

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