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10.5. Adapting to the Environment

CSS2 offers the ability to both alter the browser's environment and integrate its look more closely to that of the user's operating system.

10.5.1. Cursors

To achieve the former, we have the cursor property, which lets you declare what shape the browser's cursor will take as it passes over a given element. Want to make a humorous point about download times? Change the cursor to the wait cursor (an hourglass or watch) when the cursor passes over hyperlinks. You can even hook this property up to "cursor files" (which are not defined by the specification), so you could theoretically class your anchors based on where they go and load different icons for each type of link. For example, off-site links could cause the cursor to change into a globe, while links intended to provide help could trigger a question-mark cursor.

10.5.2. Colors

In order to let web pages more closely match the user's desktop environment, there are a whole list of new color keywords like button-highlight, three-d-shadow, and gray-text. These are all intended to use the colors of the user's operating system. In all, there are 27 of these new color keywords. I won't list them all out here, but they're listed in Table 10-1, found at the end of this chapter.

10.5.3. Outlines

While you're moving your cursor around, you might want to show where the focus is set. For example, it might be nice to define a button so that it gets a red box around it when the cursor moves over it. Well, there a number of outline properties, including outline, outline-color, outline-style, and outline-width. To use the example of a red box, you might declare:

IMG.button:hover {outline: solid red 1px;}

This should have the effect described. The outline styles could also be used to set a visible outline for regions in a client-side image map.



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Figure 7-71

Figure 7-71. Hanging float

There is one important question here, which is this: what happens to the document display when an element is floated out of its parent element by using negative margins? For example, an image could be floated so far up that it intrudes into a paragraph that has already been displayed by the user agent.

In this case, it's up to the user agent, but the CSS specifications explicitly state that user agents are not required to setting a line-height for the BIG element, the overall height of the line box has been increased, thus providing enough room for the BIG element to be displayed without overlapping any other text and without changing the line-height of all lines in the paragraph. We use a value 1em so that the line-height for the BIG element will be set to the same size as BIG's font-size -- remember,