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have a class of Baz.
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So here, I can now say, take all of the elements with a class of Baz
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and go ahead and give those a color of blue.
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So now, I have two h1s that belong to class Baz.
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The other h1 does not.
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And I've styled only the things that are of class Baz,
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such that now when I go back to the page and refresh the page, my first two
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headings, those do get styled as blue.
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But the third heading does not, because I've
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applied a class to these two elements that does not get
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applied to this third element there.
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So oftentimes, it can be very helpful if you
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have to start to design larger web pages where
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you have multiple different elements, some of which
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might be styled in some ways and other elements that might be styled similarly
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to one another, you can add IDs and classes to your HTML elements
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just to clean up the way that you write your CSS,
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to be able to very specifically pinpoint one element that you
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want to apply a style to or to apply styling to the entire class of elements
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as well.
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Now, one tricky thing you might imagine now
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is that now we have multiple ways of referencing the exact same element.
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So, for example, if you imagine that I just
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had a single h1, which had an ID of Foo, for example, that I've
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named Foo, what would happen if, for instance, I said all of the h1s I
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will like those to be colored red, and all of the elements with an ID of Foo,
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or the only element with an ID of Foo, I would like that to be colored blue?
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What might happen then?
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These would seem to be conflicting, where now suddenly we
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have an h1 style tag that is saying I should style h1s in this way,
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but I should style element Foo in another way.
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So what happens if I have an h1 whose ID is Foo, how do I choose to style that?
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And in order to deal with that we have to start
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to deal with the CSS problem of specificity, of what happens when
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I have multiple different CSS selectors that could apply to the exact same HTML
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element?
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And this often happens when we start to add IDs and classes to our elements
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as well.
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So when we deal with specificity, specificity goes in a particular order.
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There's an order of precedence that we can
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follow for determining what style should ultimately
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be applied to any particular element.
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The first, most powerful--
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most specific way of referencing an element is inline styling, literally
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adding a style equals attribute to our HTML elements
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in the way we did way at the beginning when
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we were first taking a look at CSS.
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If we associate inline styling with an HTML element, that's
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going to take precedence over any styling that's inside the style
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section of our head of the web page or inside of a separate dot CSS file,
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because the reasoning goes, if you are literally putting the style
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code attached to the element itself, then we probably
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want to apply it to that element.
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After that, specificity goes in order of how precisely we
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are identifying an element.
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An ID is a unique way to identify an element.
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There is only one element with that particular ID.
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So if I've added style to a particular ID,
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that is going to be pretty highly valued in terms of how specific it is.
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Next, we look at classes.
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So if there's no ID selector, we look for,
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did we reference the element by its class?
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And if so, then that takes next precedence.
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And otherwise, then we fall back to what type of HTML element it is.
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Is it an h1?
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Is it an ordered list?
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Is it a table?
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So in short, the type is the least specific.
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Class is slightly more specific.
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ID is more than that.
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And the most specificity we can provide is by literally putting the CSS inline
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with the HTML element itself.
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So let's take a look at an example of this.
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Let's look at this code, for example, where, for instance, I
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have a div, whose ID is Foo, inside of which I'm just saying the word hello.
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And the CSS code that I've included here is I've said for all div,
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I would like to give those a color of blue.
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Obviously, in that case, there's nothing conflicting.
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What we're going to see is we're going to see the word Hello.
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And we're going to see the word Hello in blue.
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But what happens now if we add anything with ID Foo should be colored red?
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Well, because ID has higher specificity than just an individual tag,
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well, then next, what we're going to say is that this Hello is going to show up
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is red.
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The ID is more specific.
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And so this element is going to show up red instead.
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And it doesn't matter what order these are in.
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It's not that the later one takes precedence.
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If I were to flip these around, where ID of Foo, color red, div color blue
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is in that order, it's still going to show up as red, because this ID
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selector is more specific than just the name div, which is the name of the HTML
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element that happens to be there.
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And so as you start to develop more sophisticated style sheets,
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you might find that some of your CSS code
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is going to conflict with each other.
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And that's where it's important to bear in mind how these specificity
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rules work to know as you add style to your elements
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how are they actually going to end up showing up.
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Now, we've seen a couple of CSS selectors
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now in terms of selecting a single element, selecting an ID,
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