CSS学习笔记----选择器与字体（字系）

部分来自456bereastreet

an overview of the syntax for all CSS 2.1 selectors (based on the table inCSS 2.1, 5.1 Pattern matching):

Overview of CSS 2.1 selector syntax

Selector type	Pattern	Description
Universal	*	Matches any element.
Type	E	Matches any E element.
Class	.info	Matches any element whoseclassattribute contains the valueinfo.
ID	#footer	Matches any element with anidequal tofooter.
Descendant	E F	Matches any F element that is a descendant of an E element.
Child	E > F	Matches any F element that is a child of an E element.
Adjacent	E + F	Matches any F element immediately preceded by a sibling element E.
Attribute	E[att]	Matches any E element that has anattattribute, regardless of its value.
Attribute	E[att=val]	Matches any E element whoseattattribute value is exactly equal toval.
Attribute	E[att~=val]	Matches any E element whoseattattribute value is a list of space-separated values, one of which is exactly equal toval.
Attribute	E[att|=val]	Matches any E element whoseattattribute has a hyphen-separated list of values beginning withval.
The :first-child pseudo-class	E:first-child	Matches element E when E is the first child of its parent.
The link pseudo-classes	E:link E:visited	Matches not yet visited (:link) or already visited (:visited) links.
The dynamic pseudo-classes	E:active E:hover E:focus	Matches E during certain user actions.
The :language pseudo-class	E:lang(c)	Matches elements of type E that are in language c.
The :first-line pseudo-element	E:first-line	Matches the contents of the first formatted line of element E.
The :first-letter pseudo-element	E:first-letter	Matches the first letter of element E.
The :before and :after pseudo-elements	E:before E:after	Used to insert generated content before or after an element’s content.

I’ll explain each of these selector types in more detail in this two part article, so keep reading. A few terms used in that table and in the rest of this article may need some clarification:

descendant

An element that is the child, grandchild or later descendant of an element in the document tree.

ancestor

An element that is the parent, grandparent or earlier ancestor of an element in the document tree.

child

The direct descendant of an element. No other elements may come between the two in the document tree.

parent

The direct ancestor of an element. No other element may come between the two in the document tree.

sibling

An element that has the same parent as the current element.

元素也可以基于它们的类而被选择：

td.fancy {
	color: #f60;
	background: #666;
	}

在上面的例子中，类名为 fancy 的表格单元将是带有灰色背景的橙色。

You can assign multiple class names to an element – theclassattribute can hold a space separated list of class names. Class selectors can then be used to target only elements which have several class names. This rule will matchpelements which haveboth “info” and “error” in their list of class names:

1. p.info.error { color:#900; font-weight:bold; }

Multiple attribute selectors can be used in the same selector. This makes it possible to match against several different attributes for the same element. The following rule would apply to allblockquoteelements that have aclassattribute whose value is exactly “quote”, and aciteattribute (regardless of its value):

1. blockquote[class=quote][cite] { color:#f00; }

An element may match several pseudo-classes at the same time. An element could have focus and be hovered over, for instance:

1. input[type=button]:focus {
2. color:#000;
3. background:#ffe;
4. }
5. input[type=text]:focus:hover {
6. background:#fff;
7. }

The first rule will match single lineinputelements that have focus, and the second rule will match the same elements when they are also hovered over.

属性选择器在为不带有 class 或 id 的表单设置样式时特别有用：

Each of the selectors that form a descendant selector can be a simple selector of any form. The selector in the following rule matches allpelements with a class name ofinfothat are contained by anlielement that is contained by adivelement with the idmyid.

1. div#myid li p.info { color:#f00; }

The mistake many make is to not list the full selectors. Assume that you have the following markup:

2. News

3. • Item 1
   • Item 2

Now, say you want to apply the same amount of margin to level 3 headings and unordered lists, but only if they are in thedivelement whoseidis “news”. Here is thewrongway:

1. div#news h3, ul {
2. margin:0 2em;
3. }

Thiswillaffect bothh3andulelements indiv#news. The problem is that it will targetallulelements in the document, not only those indiv#news.

Here is thecorrectway of grouping the selectors in this case:

1. div#news h3,
2. div#news ul {
3. margin:0 2em;
4. }

So, when grouping selectors, remember to fully specify each selector.

关于!important

#box {
color:red !important;
color:blue;
}

HTML

在不同的浏览器下，这行字的色应该不同！

这个例子应该是大家经常见到的important的用法了，在IE6环境下，这行字是蓝色，在IE7及firefox下，为红色。这是因为IE6不认important（即不认 !importmant 但是还是认!important前面的color:red)，并且color:blue放在color:red的后面(后面的css定义覆盖了前面的color:red)，所以在IE6下字为蓝色；而在IE7及firefox下important级别优先，所以color:red !important;和color:blue;的前后顺序没有关系，在IE7及firefox下red跟blue谁先谁后都没有关系。

我们所认为的“字体”可能有许多字体变形组成，分别用来描述粗体、斜体文本，等等。例如，你可能已经对字体 Times 很熟悉。不过，Times 实际上是多种变形的一个组合，包括 TimesRegular、TimesBold、TimesItalic、TimesOblique、TimesBoldItalic、TimesBoldOblique，等等。Times 的每种变形都是一个具体的字体风格（font face），而我们通常认为的 Times 是所有这些变形字体的一个组合。换句话说，Times 实际上是一个字体系列（font family），而不只是单个的字体，尽管我们大多数人都认为字体就是某一种字体。

除了各种特定字体系列外（如 Times、Verdana、Helvetica 或 Arial），CSS 还定义了 5 种通用字体系列：

Serif 字体

这些字体成比例，而且有上下短线。如果字体中的所有字符根据其不同大小有不同的宽度，则该字符是成比例的。例如，小写 i 和小写 m 的宽度就不同。上下短线是每个字符笔划末端的装饰，比如大写 l 顶部和底部的短线，或大写 A 两条腿底部的短线。Serif 字体的例子包括 Times、Georgia 和 New Century Schoolbook。

Sans-serif 字体

这些字体是成比例的，而且没有上下短线。Sans-serif 字体的例子包括 Helvetica、Geneva、Verdana、Arial 或 Univers。

Monospace 字体

Monospace 字体并不是成比例的。它们通常用于模拟打字机打出的文本、老式点阵打印机的输出，甚至更老式的视频显示终端。采用这些字体，每个字符的宽度都必须完全相同，所以小写的 i 和小写的 m 有相同的宽度。这些字体可能有上下短线，也可能没有。如果一个字体的字符宽度完全相同，则归类为 Monospace 字体，而不论是否有上下短线。Monospace 字体的例子包括 Courier、Courier New 和 Andale Mono。

Cursive 字体

这些字体试图模仿人的手写体。通常，它们主要由曲线和 Serif 字体中没有的笔划装饰组成。例如，大写 A 再其左腿底部可能有一个小弯，或者完全由花体部分和小的弯曲部分组成。Cursive 字体的例子包括 Zapf Chancery、Author 和 Comic Sans。

Fantasy 字体

这些字体无法用任何特征来定义，只有一点是确定的，那就是我们无法很容易地将其规划到任何一种其他的字体系列当中。这样的字体包括 Western、Woodblock 和 Klingon。

看了这些，终于知道Chrome的字体设置里面那么多选项是什么意思了，哈哈!