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CSS gives Web designers control over the appearance of their web sites by separating the visual presentation from the content. It lets them easily make minor changes to a site or perform a complete overhaul of the design. In CSS Web Site Design, instructor and leading industry expert Eric Meyer reviews the essentials of CSS, including selectors, the cascade, and inheritance. The training also covers how to build effective navigation, how to lay out pages, and how to work with typography, colors, backgrounds, and white space. Using a project-based approach, Eric walks through the process of creating a Web page, while teaching the essentials of CSS along the way. By the end of the training, viewers will have the tools to master professional site design. Exercise files accompany the training videos.
As you just saw in the previous video, you can not only place an image in the background of an element, you can also affect the way it repeats, you can have it repeat horizontally, vertically or not repeat at all. Now, what we're going to look at in this video, is how you can effect the placement of that image an we're going to do that with our little no repeated image here, or nonrepeated image up, in the upper left-hand quarter of the content. Let's say a background position top. This is not the end of what we can do, but it's a good place to restart. We hit Reload, the, tadaa! The image goes right into the center of the top of the elements background. If you only have one keyword and this is a keyword top, then it's assumed that the one that you didn't provide is center. So there are five keywords in that position, there're top, bottom, right, left and center. So I could say top center, and that would be exactly the same as just saying top, because if I don't have that second keyword, then center is assumed. If I change this to say right, then the browser would assume that I wanted it in the right center. You can see it's over there on the right edge in the vertical center of the element, not the center of the page.
The center of the element. So our center element is, that's been lined up with the midpoint, the vertical midpoint of that element. OK, now, this is equivalent, this top or top center, can be expressed in different ways. I can say 50% 0. What that means is take this element and put it 50% of the way across the element and 0 down, so don't push it down at all, just put it 50% of the way across and that comes out to be basically top center, 50% and was actually having as the midpoint of that image is lined up with the midpoint of the element and then in the case of zero is just not pushed down at all.
It can be. The thing is that the order matters here. When it comes to numbers, the order matters. With the keywords you can center top or top center, doesn't matter it's still going to end up in that top center area, but with the numbers it's always the horizontal position first and the vertical position second. If I reverse this, I'm saying don't push the background image over at all, but but align it vertically, at the 50% point, and you'll to see that this is going to flip over to the left center. Because, again, with the numbers, the order matters. If I want it top center, I got to say 50% zero. So only if I just set 75%, and I don't provide another number, that's the horizontal position, that's going to place the image three quarters of the way across the element and 50% down. So, 50% being in the mid, vertical midpoint of that element, so you can see there it is, its three quarters of the way across and vertically it's centered, it's up to 50% point because, when I have a number like this, when I just 75% it's assumed that the other number is 50% and since the horizontal always comes first, that means that a vertical 50% is always assumed.
Now we don't have to always stick to percentages, I could say I want this to be 75% of the way across and 50 pixels down from the top. So there, the top edge of that background image is going to be 50 pixels below the top edge of the element and is going to be three quarters of the way across the element. Now the fact that the image bottom happens to line up with the boarder, there that is a total coincidence. If I were to change the text size, then you can see that alignment doesn't actually exist. That's completely an illusion, just happens to have landed there.
Now, where this get's interesting is if we do actual repetition. So suppose I say repeat-x from my background position of 75% 50 pixels. I say repeat along the x-axis and it does. Repeat x doesn't mean repeat right, it actually means repeat in both directions along the x-axis. So from that placement of 75% 50px, which is right where it was before, the image is tiled out horizontally in both directions.
And if I flip it so that I'm actually doing repeat-y instead of repeat-x, and again, from that position, from that placement, it repeats in both directions, both upwards and downwards along the y-axis. There's no such thing as repeat down in CSS. There's only repeat-y and it goes in both directions here. So, why that makes a difference, you can actually see, if I were to say repeat-y top center, that's going to move this so that the origin image, which is the placement of the first image is in the top center, just like we saw before and then it's tiled vertically in both directions.
Bu that means, effectively, it's visually justified to the top of the element background and if I were to change this to le's say just center, then watch over here what it happens when I hit Reload. See how there is that slight change. What's happened now is that this straight is being centered, because the origin image, the first placement is right in the middle of the element and that's repeated in both directions. You get the stripe effectively visually centered within the element background so there's a little bit of, of images, of visible at the top of the element background, a little bit visible at the bottom of the background. So that's why there's a difference in where you position the background image and then you tile it. It is exactly the same thing if we were to do a full on repeat, which we can do if the background position is centered and then we just repeat. The tiling is centered within the element effectively, so no matter how we change the size of the browser window, the pattern always stays centered within the element, whereas if I were to take this back to the let's say top left or 00, which is the default value, then the origin image is going to be the top left corner and no matter how that element changes size, The painting is always anchored to that, background is always anchored to that top left corner. So, there's how background positioning can actually affect the way that the tiling looks in a web browser.
In the next exercise we're going to take a look at how we can bring all this down effectively into a very simple expression.
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