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CSS: Page Layouts introduces basic layout concepts, gives advice on how to create properly structured HTML based on prototypes and mockups, and goes into critical page layout skills such as floats and positioning. Author James Williamson shows how to combine these techniques to create fixed, fluid, and responsive layouts. Designers are also shown how to enhance their pages through the creative use of CSS techniques like multi-column text, opacity, and the background property. Exercise files are included with this course.
Earlier in this chapter, we saw one of the unfortunate side effects of floating elements. Remember, floated elements are removed from normal flow. That means that the height of their parent elements then collapse as if the floated elements inside them simply weren't there. This can cause a whole host of undesirable results, such as disappearing backgrounds and overlapping content. Now, fortunately, we have a few ways to prevent this from happening. So we have the containing.htm file open, and you can find that in the 03_03 folder.
If I scroll down just a little bit, you can see that we have a section. Inside that we have three divs, with the classes One, Two, and Three. If I were to preview just the default styles in a browser, you can see these elements are just stacking, normal document flow, one on top of each other: One, Two, and Three. Well, currently the height of the section is being controlled by the elements inside of it. That's actually quite common. Height is generally considered unless it's set explicitly to be auto. That means the contents of an element define its height.
So once we float these elements and remove them from normal flow, then section really doesn't have any height and it's just going to collapse. So I am going to go back into my code, and what I am going to do is, each one of these div tags, One, Two, and Three, I am just going to go ahead and float those to the left. So I am going to do that for each of them, so that we can observe the parent collapsing. So I am going to go back into the browser, refresh the page, and you can see that's exactly what's happening now: One, Two, and Three are floating.
They're removed from normal document flow. Section doesn't see it inside of it anymore, and so it collapses. And in fact, the only thing we're seeing here right now, guys, is the padding that's set inside the section. So let's take a look at a couple of ways that we can help contain those floated elements inside the section. Okay. So if I go back into my code, well, one of the ways to do this is if you have an element that's underneath your floated elements and you clear that to restore normal document flow, then the parent container will go all the way down to contain it as well.
So if I go down here and right past the last div tag I add another paragraph, and inside of that paragraph I can just say "Clearing floats help to contain them," so if I save this, and I can just come right up here and create another selector for the paragraph and just tell that to clear: both. We added a new element underneath our floated elements, and then we told that element to clear, meaning reestablish normal flow.
So if I go back into my browser and refresh that, you can see what happens. Our paragraph shows up down here. It's cleared, meaning normal flow is reestablished, and our section is now extending down to contain that, so that's one way of containing it. Of course to do that we have to have another element below our floated elements, and that's not always going to be the case with your layouts. So there are a couple of other methods that you can use. Let's take a look at those. So if I come back into my code, I am going to get rid of that paragraph, selector and the paragraph itself, there we go. And what I am going to do is I am going to go up to the section selector, the one that's controlling its styling, and I am going to use the overflow property.
Now, the overflow property is a property that basically tells the browser what to do when the contents of a box no longer fit inside of it. So we have a few options available to us. Hidden is one. Hidden just says, hey, clip off any content that overflows. Auto would create scrollbars, either horizontally or vertically, based upon the flow of the content. And Scroll will force scrollbars in. Visible, by the way, just causes that content to be visible and overlap. Well, there is a side effect to using overflow.
So I am going to type in overflow: hidden. Now, anything other than Visible will work with it, so it could be Hidden, Auto, or Scroll. Now, obviously Scroll is going to force scrollbars to show up, and you don't want that. Auto will work, and it will work almost all the times with no side effects, but occasionally you're going to have a time when scrollbars show up for just weird reasons, because the floated elements inside of it perhaps are forcing a certain amount of auto flow. So by saying overflow: hidden, we're essentially saying, hey, we want to set overflow on this element, but we don't want any scrollbars to show up.
So if I save this and test it, now even without the extra content in the div tag, the float is being contained and that's the overflow property that is doing that for us. That's going to work for you about say 90% of the time, but there are going to be certain times when that overflow: hidden property is going to come back to bite you. Let me show you what I mean. So if I go back into my code, let's say I take the third div tag here, and I apply something relatively new, like box-shadow. So if I do box-shadow--now, when you're doing a box-shadow, that's just really, it's sort of a drop-shadow for this div tag.
So I am going to give 10-pixel offset to the X, 10-pixel Y offset, give it a 10-pixel blur, 10-pixel spread, and then the color for the shadow I will just go ahead and make that black, so #000. If I save this--and those are really high offsets, but I really wanted you to be able to see this, if I go back into the browser and load that up, you can see what's happening. Our drop shadow is showing up, but because the section has overflow set to hidden, it's going to hide this portion of the box shadow.
It's not going to expand to fill that. So there are times when overflow: hidden, even though it will contain floats for you, is going to give you some negative side effects. We do have one more technique that can work for us. So I am going to go ahead and get rid of the box-shadow. I am going to go ahead and get rid of overflow: hidden, and I want to modify one last little thing here. You will notice, for example, that body has a background color of white and a width of 600 pixels. So I am going to take the section and I am going to set its width to say 480 pixels.
Now, why am I doing that? Well, if I save this, and if I preview this in my browser, you can see now the section is actually not as wide as body, and you can also see that body sort of has that white background color here. Why am I doing that? Well, another method that you can use to contain floats is that if you float the parent element, meaning the container element, if you float that one as well, all floats inside of that will also be contained. So if I take section and I apply float: left to it as well, save that, and preview that in the browser, you can see what happens.
The float is now contained. But it sort of has a chain reaction. You'll notice, for example, that the body tag is now collapsing as well. We no longer see that white background because all of the content inside of it is now floated, and so it collapses. So a lot of times that works, but you end up having to go back through your layout and clear all these other items that you wouldn't have to clear previously. So it's not always the right answer either. So we've seen three ways that allow us to prevent container collapsing. We can clear child elements that appear below floated elements.
We can set the overflow property of the parent container to either Hidden, Auto, or Scroll. Or we can set a float value on the containing element itself. Now, as we've seen, each one of these methods have their pros and their cons, and you're going to have to very carefully consider when they're appropriate within your own layouts. Now, personally, I use either one of two methods: I will either use the overflow: hidden method, which is going to contain my floats, or I am going to use a clearing method for containing all the elements that have floated children, so clearing an element below it.
Now, specifically, I use a method called clearfix, because the method I showed you in this particular example requires there an element to be underneath it, but the clearfix method doesn't. Now, since the syntax of clearfix needs a little bit of explanation, we're going to go ahead and discuss that in a separate movie next.
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