What is the difference between css selector pound sign and period?

CSS里的样式表是有规则组成的，每条规则有三个部分组成：
1、选择器（如下面例子中的：“body”），告诉浏览器文档的哪个部分受规则影响；
2、属性（如实例中的font-family、color等），规定了布局的什么方面被设置了；
3、值（如实例中的Arial,sans-serif，#333333等），给出了式样属性的值。
 #是ID选择器 .是class选择器 *是通配符号 
比如*{margin：0；padding：0；所有的元素都会沿用这个属性样式}（还有一种情况是IE hack）比如 .b{margin:0;*margin:10px;}这里IE看到的是margin：10px，其他的浏览器看到的会是前面那个margin：0；

Let’s look at the code first~

body{
font-family: Arial,sans-serif;
color: #333333;
line-height: 1.166; 
margin: 0px;
 padding: 0px;
}
#masthead{
margin: 0;
padding: 10px 0px;
border-bottom: 1px solid #cccccc;
width: 100%;
}
.feature img{
float: left;
padding: 0px 10px 0px 0px;
 margin: 0 5px 5px 0;
}

# corresponds to the id
The dot corresponds to class
No corresponding html tags
It can be summed up in one sentence: Class can be used repeatedly but ID can only be used once in a page. It's possible that using the same ID repeatedly will not cause problems in a large number of browsers, but this is definitely an incorrect use according to the standard, and may cause real-life problems in some browsers.
In actual application, Class may be more useful for text layout, etc., while ID is more useful for macro layout and design placement of various elements.

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