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So I can say let me add 5 pixels worth of padding
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inside of all of my table data cells and table header cells.
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Refresh the page.
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And now, here's what the resulting table looks like.
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Just by adding a little bit of CSS specifying what
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border I want around the edge of the page,
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specifying a little bit of padding inside of each of the cells,
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my table now looks a whole lot nicer than it did just a few lines of code
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ago when I just had the HTML structure of the page and not the CSS
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to describe how I actually wanted that page to be styled.
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And notice again that in doing so, we were
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able to use one of these CSS selectors.
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I was able to say that I wanted to use the multiple element selector, which
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is just this comma here, to specify that I would like to apply this styling,
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not just to td's but also to th's as well.
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We'll take a look at some additional examples of CSS selectors
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in just a moment.
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But next, let's turn our attention to some more tricky instances
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where we might want to apply styling to multiple elements at the same time.
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Let's imagine-- and let's go back to style.html, where we had some style
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code, where I had one heading.
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I'll call this Heading 1.
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And let's get myself to other headings, Heading 2 and Heading 3.
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All of these now are h1 elements that are going to show up the same way,
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such that now if I style and say, I would like all h1s to show up with
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a color of blue, then when I open this page where I have three h1 tags,
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each of which has a color of blue, when I open up style.html,
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what I'm going to see is something like this--
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three headings, each of which happens to have a color of blue.
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But what would happen now if I wanted to style only the first heading.
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I want Heading 1 to be blue.
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But I don't want to style Heading 2 and Heading 3.
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How do I do that?
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Well, one thing we could do is go back to the inline styling
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we did a moment ago, where inside of h1, I said style color is blue.
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And that would say for just this very first heading,
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I would like that to be blue, but not the other elements at all.
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But this again we decided was not the best design.
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This inline styling, commingling of HTML and CSS just gets a little bit messy.
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And it would be nice to be able to factor all of our style code
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to a separate part of the page altogether.
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So how do we do this?
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Well, we need some way to uniquely reference this particular HTML element.
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And in order to do so, we can given HTML element an ID.
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An ID is just some unique name we give to an HTML element,
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so that we can reference it more easily later on.
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Let me just go ahead and give this an ID of Foo.
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It could be any idea you want.
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But Foo is just a generic name here.
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And now, we've given this heading a name such that in other parts of our page
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or in other code, we can reference and find this particular HTML element.
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And in particular now, in the style section of my web page,
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instead of styling all h1 elements, I only want to style
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the element that has an ID of Foo.
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IDs are by definition unique.
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There can only be one element in this page that has an ID of Foo,
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otherwise it's not valid HTML.
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And so in order to do so, we're going to use #Foo.
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The hash mark symbol is just CSS's way of selecting just something
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with a particular ID.
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So instead of just h1 for selecting all of the h1 tags,
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if I want to select something by its ID, I
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say #Foo to say only style the element that has an ID of Foo
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and give it a color of blue, for example.
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So this style code now will find something with a particular ID
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and give it a style to correspond with it,
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such that now if I reload this page, only Heading 1 is styled.
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Heading 2 and Heading 3 are not.
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I've been able to name Heading 1, give it a name of Foo, an ID of Foo,
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and then in my style code, just style that particular part of my HTML page.
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Of course, what if I wanted to style multiple, but not all of the headings?
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Like maybe I want to style both Heading 1 and Heading 2.
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Now, I could use a second ID.
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Maybe give us an ID of Bar, for example.
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And then style both the element with ID Foo and the element with ID Bar.
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But now we're starting to add IDs unnecessarily.
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I have too many different names.
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Things can start to get messy, especially
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as my web pages start to get bigger.
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So while IDs are a way of giving a name to an HTML element that is unique,
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sometimes I want to give a name to an HTML element that is not unique,
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some name that can apply to multiple different HTML elements.
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And when we do that, we call that a class.
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An ID is a way of giving a unique name to an HTML element,
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while a class is a way of giving a name to an HTML element that
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might not be unique.
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It might apply it to zero or one or two or more different HTML elements.
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So here's what that might look like.
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Instead of giving each of these h1s an ID that's different,
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I can give each one a class.
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We'll give this a class of Baz, again, just another arbitrary name
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that we've chosen.
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And I'll give this each one a class of Baz as well.
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They both belong to the same class called Baz, in this case.
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And now, inside of my style code, I would like to say just the style
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the elements that are of class Baz.
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And just as we have a special symbol, the hashtag,
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for styling definitely something with a particular ID,
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to style everything with a particular class, I can use a dot.
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So dot Baz, in this case, is going to style only the elements that
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