Book HomeCascading Style Sheets: The Definitive GuideSearch this book Thursday 14th of December 2017 01:54:05 PM

9.4. Fixed Positioning

As one border style. So don't try to declare more than one valuetype:

H3 {border: thin thick solid purple;}  /* two width values--WRONG */

In such a case, the entire statement will be invalid and should beignored altogether.

Finally, you need to take the usual precautions with shorthandproperties: if you omit a value, the default will be filled inautomatically. This can have unintended effects. Consider the implied in the previous section, fixed positioning is just like absolute positioning, except the containing block of a fixed element is always the viewport. In this case, the element is totally removed from the document's flow and does not have a position relative to any part of the document.

This can be exploited in a number of interesting ways. First off, it's possible to create frame-style interfaces using fixed positioning. Consider Figure 9-24, which shows a very common layout scheme.

Figure 9-24

Figure 9-24. Emulating frames with fixed positioning

This could be done using the following styles:

DIV#header {position: fixed; top: 0; bottom: 80%; left: 20%; right: 0;
background: gray;}
DIV#sidebar {position: fixed; top: 0; bottom: 0; left: 0; right: 80%;
background: silver;}

This will fix the header and sidebar to the top and side of the viewport, where they will remain regardless of how the document is scrolled. The drawback here, though, is that the rest of the document will be overlapped by the fixed elements. Therefore, the rest of the content should probably be contained in its own DIV and employ the following:

DIV#main {position: absolute; top: 20%; bottom: 0; left: 20%; right: 0;
overflow: scroll; background: white;}

It would even be possible to create small gaps between the three positioned DIVs by adding some appropriate margins, demonstrated in Figure 9-25:

BODY {background: black; color: silver;}  /* colors for safety's sake */
DIV#header {position: fixed; top: 0; bottom: 80%; left: 20%; right: 0;
background: gray; margin-bottom: 2px; color: yellow;}
DIV#sidebar {position: fixed; top: 0; bottom: 0; left: 0; right: 80%;
background: silver; margin-right: 2px; color: maroon;}
DIV#main {position: absolute; top: 20%; bottom: 0; left: 20%; right: 0;
overflow: scroll; background: white; color: black;}
Figure 9-25

Figure 9-25. Separating the "frames"

Given such a case, a tiled image could be applied to the BODY background. This image would show through the gaps created by the margins, which could certainly be widened if the author saw fit. For that matter, if a background image was of little importance, simple borders could be applied to the DIVs instead of margins.



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normal | bold | bolder | lighter | 100 | 200 | 300 | 400 | 500 | 600 | 700 | 800 | 900

Default

normal

Inherited

yes

Applies to

all elements

LI.first {list-style-position: inside;}

This causes the bullet to be placed "inside" the list item's content. The exact way this happens is undefined, but Figure 7-86 shows one possibility.

Figure 7-86

Figure 7-86. Placing the bullets inside and outside list items

CSS2, by the way, provides a good deal more control over the positioning of the bullets (called "markers" in CSS2); again, this is discussed in Chapter 10, "CSS2: A Look Ahead".