6. CSS box model hack alternative
The box model hack is used to fix a rendering problem in pre-IE 6 browsers on PC, where by the border and padding are included in the width of an element, as opposed to added on. For example, when specifying the dimensions of a container you might use the following CSS rule:
#box
{
width: 100px;
border: 5px;
padding: 20px
}
This CSS rule would be applied to:
<div id="box">...</div>
This means that the total width of the box is 150px (100px width + two 5px borders + two 20px paddings) in all browsers except pre-IE 6 versions on PC. In these browsers the total width would be just 100px, with the padding and border widths being incorporated into this width. The box model hack can be used to fix this, but this can get really messy.
A simple alternative is to use this CSS:
#box
{
width: 150px
}
#box div
{
border: 5px;
padding: 20px
}
And the new HTML would be:
<div id="box"><div>...</div></div>
Perfect! Now the box width will always be 150px, regardless of the browser!
7. Centre aligning a block element
Say you wanted to have a fixed width layout website, and the content floated in the middle of the screen. You can use the following CSS command:
#content
{
width: 700px;
margin: 0 auto
}
You would then enclose <div id="content"> around every item in the body of the HTML document and it'll be given an automatic margin on both its left and right, ensuring that it's always placed in the centre of the screen. Simple... well not quite - we've still got the pre-IE 6 versions on PC to worry about, as these browsers won't centre align the element with this CSS command. You'll have to change the CSS rules:
body
{
text-align: center
}
#content
{
text-align: left;
width: 700px;
margin: 0 auto
}
This will then centre align the main content, but it'll also centre align the text! To offset the second, probably undesired, effect we inserted text-align: left into the content div.
8. Vertically aligning with CSS
Vertically aligning with tables was a doddle. To make cell content line up in the middle of a cell you would use vertical-align: middle. This doesn't really work with a CSS layout. Say you have a navigation menu item whose height is assigned 2em and you insert this vertical align command into the CSS rule. It basically won't make a difference and the text will be pushed to the top of the box.
Hmmm... not the desired effect. The solution? Specify the line height to be the same as the height of the box itself in the CSS. In this instance, the box is 2em high, so we would insert line-height: 2em into the CSS rule and the text now floats in the middle of the box - perfect!
9. CSS positioning within a container
One of the best things about CSS is that you can position an object absolutely anywhere you want in the document. It's also possible (and often desirable) to position objects within a container. It's simple to do too. Simply assign the following CSS rule to the container:
#container
{
position: relative
}
Now any element within this container will be positioned relative to it. Say you had this HTML structure:
<div id="container"><div id="navigation">...</div></div>
To position the navigation exactly 30px from the left and 5px from the top of the container box, you could use these CSS commands:
#navigation
{
position: absolute;
left: 30px;
top: 5px
}
Perfect! In this particular example, you could of course also use margin: 5px 0 0 30px, but there are some cases where it's preferable to use positioning.
10. Background colour running to the screen bottom
One of the disadvantages of CSS is its inability to be controlled vertically, causing one particular problem which a table layout doesn't suffer from. Say you have a column running down the left side of the page, which contains site navigation. The page has a white background, but you want this left column to have a blue background. Simple, you assign it the appropriate CSS rule:
#navigation
{
background: blue;
width: 150px
}
Just one problem though: Because the navigation items don't continue all the way to the bottom of the screen, neither does the background colour. The blue background colour is being cut off half way down the page, ruining your great design. What can you do!?
Unfortunately one of the only solutions to this is to cheat, and assign the body a background image of exactly the same colour and width as the left column. You would use this CSS command:
body
{
background: url(blue-image.gif) 0 0 repeat-y
}
This image that you place in the background should be exactly 150px wide and the same blue colour as the background of the left column. The disadvantage of using this method is that you can't express the left column in terms of em, as if the user resizes text and the column expands, it's background colour won't.
Using this method the left column will have to be expressed in px if you want it to have a different background colour to the rest of the page.
