1. More CSS
22-Feb-19

2. A different emphasis
CSS is the same for XML as it is for HTML and XHTML, but--
XML contains no display information
If you want your XML to be easily read by humans, you need CSS
You need to take charge of arranging text on the page
HTML can use tables for layout
In XHTML you should use CSS (but tables are much easier)
In XML you don’t have tables
Some browsers, especially older versions of IE, don’t support CSS very well, so:
You should make sure everyone who views your pages uses the same version of the same browser (this is possible in some companies), or
You should test your pages in all the most common browsers

3. The display property
Every element that is formatted by a CSS command is considered to be in an invisible “box”
The box containing an element can have one of three display properties:
display: block
The element will start on a new line, and so will the element that follows it (an HTML paragraph is an example)
display: inline
(default) The element will not start on a new line, or cause the next element to start on a new line (bold is an HTML example)
display: none
The element is hidden and will not appear on the display

4. CSS units
For many of the remaining CSS values, we will need to be able to specify size measurements
These are used to specify sizes:
em width of the letter ‘m’
ex height of the letter ‘x’
px pixels (usually 72 per inch, but depends on monitor)
% percent of inherited size
These are also used to specify sizes, but don’t really make sense unless you know the screen resolution:
in inches
cm centimeters
mm millimeters
pt points (72pt = 1in)
pc picas (1pc = 12pt)
Note: you can use decimal fractions, such as 1.5cm

5. border (can be colored)
Boxes
The invisible box containing a styled element has three special areas:
margins (invisible)
border (can be colored)
padding (invisible)
The element

6. Padding
Padding is the extra space around an element, but inside the border
To set the padding, use any or all of:
padding-top: size
padding-bottom: size
padding-left: size
padding-right: size
padding: size to set all four sides at once
size is given in the units described earlier
Example: sidebar {padding: 1em; padding-bottom: 5mm}

7. Borders
You can set border attributes with any or all of: border-top:, border-bottom:, border-left:, border-right:, and border: (all at once)
The attributes are:
The thickness of the border: thin, medium (default), thick, or a specific size (like 3px)
The style of the border: none, dotted, dashed, solid, double, groove, ridge, inset, or outset
The color of the border: one of the 16 predefined color names, or a hex value with #rrggbb or rgb(r, g, b) or rgb(r%, g%, b%)
Example: section {border-top: thin solid blue;}
Note: the special styles (such as groove) are not as cool as they sound

8. Margins Margins are the extra space outside the border
Setting margins is analogous to setting padding
To set the margins, use any or all of:
margin-top: size
margin-bottom: size
margin-left: size
margin-right: size
margin: size to set all four sides at once

9. Box and display interactions
With display:none, contents are invisible and margin, border, and padding settings have no effect
With display:block, margin, border, and padding settings work about as you would expect
With display:inline (which is the default if you don’t specify otherwise):
Margin, border, and padding settings for left and right work about as you would expect
Margin, border, and padding settings for top and bottom do not add extra space above and below the line containing the element
This means that inline boxes will overlap other text

10. Sizing elements
Every element has a size and a natural position in which it would be displayed
You can set the height and width of display:block elements with:
height: size
width: size
You cannot set the height and width of inline elements (but you can set left and right margins)
In HTML, you can set the height and width of images and tables (img and table tags)

11. Setting absolute position
position:absolute; left: 0in; top: 0in
position:absolute; right: 0in; top: 0in
position:absolute; left: 0in; bottom: 0in
position:absolute; right: 0in; bottom: 0in
Setting absolute position
To move an element to an absolute position on the page
position: absolute (this is required!) and also one or more of
left: size or right: size
top: size or bottom: size
Confusing stuff:
size can be positive or negative
top: size puts an element’s top size units from the page top
bottom: size puts an element’s bottom size units from the page bottom
left: size puts an element’s left side size units from the left edge of the page
right: size puts an element’s right side size units from the right edge of the page
Changing an element’s absolute position removes it from the natural flow, so other elements fill in the gap
You need to be careful not to overlap other elements

12. Setting relative position
To move an element relative to its natural position, use
position: relative (this is required!) and also one or more of
left: size or right: size
top: size or bottom: size
Confusing stuff:
size can be positive or negative
to move left, make left negative or right positive
to move right, make right negative or left positive
to move up, make top negative or bottom positive
to move down, make bottom negative or top positive
Setting an element’s position does not affect the position of other elements, so
There will be a gap in the element’s original, natural position
Unless you are very careful, your element will overlap other elements

13. Pseudo-elements
Pseudo-elements describe “elements” that are not actually between tags in the XML document
Syntax: element:pseudo-class {...}
first-letter the first character in a block-level element
first-line the first line in a block-level element (depends on the browser’s current window size)
Especially useful for XML (but not implemented in Internet Explorer):
before adds material before an element
Example: author:before {content: "by "}
after adds material after an element

14. External style sheets
In HTML, within the <head> element: <link REL="STYLESHEET" TYPE="text/css" HREF="Style Sheet URL">
As a PI in the prologue of an XML document: <?xml-stylesheet href="Style Sheet URL" type="text/css"?>
Note: "text/css" is the MIME type

15. Namespace selectors
Namespace selectors (XML only) choose tags from the given namespace
namespace|element {...} chooses the element if and only if it is from the given namespace
*|element {...} chooses the element regardless of the namespace
|element {...} chooses the element if it has no declared namespace
Namespace selectors are currently supported only by Netscape 6

16. Some border styles and values
You can put borders around elements
Borders have width, style, and color
These can be set individually:
border-left-style:, border-bottom-color:, etc.
Or a border at a time:
border-top:, border-right:, etc.
Or all borders at once: border:
Available values are:
border-width: thin | medium | thick | length
border-style: none | hidden | dotted | dashed | solid | double | groove | ridge | inset | outset
border-color: color

17. But wait! There’s more...
In this and the preceding lectures, I’ve covered some of the more commonly useful parts of CSS
(In other words, the parts I’ve been using)
There are other features I haven’t touched on

18. The End