1. Use CSS abbreviations.
Using abbreviations can help reduce the size of your CSS files and make them easier to read. For the main rules of CSS abbreviation, please refer to "Common CSS Abbreviation Syntax Summary", which will not be described here.
2. Define the unit clearly, unless the value is 0.
Forgetting to define the unit of the size is a common mistake among CSS novices. In HTML you can just write width="100", but in CSS you have to give an exact unit, such as: width:100px width:100em. There are only two exceptions for not defining units: row height and 0 value. In addition, other values must follow the unit. Be careful not to add spaces between the value and the unit.
3. Case Sensitivity
When using CSS in XHTML, the element names defined in CSS are case sensitive. To avoid this error, I recommend using lowercase for all definition names.
The values of class and id are also case-sensitive in HTML and XHTML. If you must write mixed case, please carefully confirm that your definition in CSS is consistent with the tags in XHTML.
4. Cancel the element qualification before class and id
. When you write to define class or id for an element, you can omit the previous element qualification, because ID is unique in a page, and class s can be used multiple times in the page. It makes no sense for you to qualify an element. For example:
div#content { /* declarations */ }
fieldset.details { /* declarations */ }
Can be written as #content { /* declarations */ }
.details { /* declarations */ }
This saves some bytes.
5. Default value
Usually the default value of padding is 0, and the default value of background-color is transparent. But the default value may be different in different browsers. If you are afraid of conflicts, you can define the margin and padding values of all elements to be 0 at the beginning of the style sheet, like this:
* {
margin:0;
padding:0;
}
6. There is no need to repeatedly define inheritable values.
In CSS, child elements automatically inherit the attribute values of the parent element, such as color, font, etc., which have been defined in the parent element, can be directly inherited in the child element, and do not need to be repeated. definition. But be aware that the browser may override your definition with some default values.
7. The nearest-first principle.
If there are multiple definitions of the same element, the closest (minimum level) definition will take precedence. For example, there is this piece of code Update: Lorem ipsum dolor set
In the CSS file, you have defined the element p and a class "update"
p {
margin:1em 0;
font-size:1em;
color:#333;
}
.update {
font-weight:bold;
color:#600;
}
Of these two definitions, class="update" will be used because class is closer than p. You can check out W3C's "Calculating a selector's specificity" to learn more.
8. Multiple class definitions
A label can define multiple classes at the same time. For example: We first define two styles, the first style has a background of #666; the second style has a 10 px border.
.one{width:200px;background:#666;}
.two{border:10px solid #F00;}
In the page code, we can call <div class="one two"></div> like this
The final display effect is that this div has both a #666 background and a 10px border. Yes, it is possible to do this, you can try it.
9. Use descendant selectors.
CSS beginners don’t know that using descendant selectors is one of the reasons that affects their efficiency. Subselectors can help you save a lot of class definitions. Let's take a look at the following code:
<div id="subnav">
<ul>
<li class="subnavitem"> <a href="#" class="subnavitem">Item 1</a></li>>
<li class="subnavitemselected"> <a href="#" class="subnavitemselected"> Item 1</a> </li>
<li class="subnavitem"> <a href="#" class="subnavitem"> Item 1</a> </li>
</ul>
</div>
The CSS definition for this code is:
div#subnav ul { /* Some styling */ }
div#subnav ul li.subnavitem { /* Some styling */ }
div#subnav ul li.subnavitem a.subnavitem { /* Some styling */ }
div#subnav ul li.subnavitemselected { /* Some styling */ }
div#subnav ul li.subnavitemselected a.subnavitemselected { /* Some styling */ }
You can replace the above code with the following method<ul id="subnav">
<li> <a href="#"> Item 1</a> </li>
<li class="sel"> <a href="#"> Item 1</a> </li>
<li> <a href="#"> Item 1</a> </li>
</ul>
The style definition is:
#subnav { /* Some styling */ }
#subnav li { /* Some styling */ }
#subnav a { /* Some styling */ }
#subnav .sel { /* Some styling */ }
#subnav .sel a { /* Some styling */ }
Use subselectors to make your code and CSS more concise and easier to read.
10. There is no need to add quotes to the background image path
. In order to save bytes, I recommend not to add quotes to the background image path, because the quotes are not necessary. For example:
background:url("images/***.gif") #333;
It can be written as background:url(images/***.gif) #333;
If you add quotation marks, it will cause some browser errors.
11. Group selectors (Group selectors)
When some element types, classes or ids have some attributes in common, you can use group selectors to avoid multiple repeated definitions. This can save quite a few bytes.
For example: to define the font, color and margin of all titles, you can write:
h1,h2,h3,h4,h5,h6 {
font-family:"Lucida Grande",Lucida,Arial,Helvetica,sans-serif;
color:#333;
margin:1em 0;
}
If there are individual elements that need to define independent styles during use, you can add new definitions or overwrite old definitions, for example:
h1 { font-size:2em; }
h2 { font-size:1.6em; }
12. Specify link styles in the correct order.
When you use CSS to define multiple state styles of a link, pay attention to the order in which they are written. The correct order is: :link :visited :hover :active. The first letter extracted is "LVHA", which you can remember as "LoVe HAte" (like it or hate it). Why is it so defined? You can refer to Eric Meyer's "Link Specificity".
If your users need to use keyboard control and need to know the focus of the current link, you can also define the :focus attribute. The effect of the :focus attribute also depends on the position where you write. If you want the focused element to display the :hover effect, you write :focus before :hover; if you want the focus effect to replace the :hover effect, you put :focus After :hover.
13. Clear floats.
A very common CSS problem is that when floating is used for positioning, the underlying layer is covered by the floating layer, or the sub-layers nested in the layer exceed the scope of the outer layer.
The usual solution is to add an extra element behind the floating layer, such as a div or a br, and define its style as clear: both. This method is a bit far-fetched, but fortunately there is a good way to solve it. Please refer to this article "How To Clear Floats Without Structural Markup" (Note: This site will translate this article as soon as possible).
The above two methods can solve the problem of floating overflow very well, but what if you really need to clear the layer or the objects in the layer? A simple method is to use the overflow attribute. This method was originally published in "Simple Clearing of Floats" and has been widely discussed in "Clearance" and "Super simple clearing floats".
Which of the above clear methods is more suitable for you depends on the specific situation and will not be discussed here. In addition, some excellent articles have made it very clear about the application of float. It is recommended that you read: "Floatutorial", "Containing Floats" and "Float Layouts"
14. Horizontal centering (centering)
This is a simple technique, but it is worth saying again, because I see too many novice questions asking this: How to center CSS horizontally? You need to define the width of the element, and define the horizontal margin, if your layout is contained in a layer (container), like this:
You can define it to be horizontally centered like this:
#wrap {
width:760px; /* Change to the width of your layer*/
margin:0 auto;
}
But IE5/Win cannot display this definition correctly. We use a very useful trick to solve it: use the text-align attribute. Like this:
body {
text-align:center;
}
#wrap {
width:760px; /* Change to the width of your layer*/
margin:0 auto;
text-align:left;
}
The first body's text-align:center; rule defines that all elements of the body in IE5/Win are centered (other browsers just center the text), and the second text-align:left; is to center the text in #warp to the left.
15. Import and hide CSS.
Because older browsers do not support CSS, a common approach is to use the @import technique to hide CSS. For example:
@import url("main.css");
However, this method didn't work for IE4, which gave me a headache for a while. Later I wrote it like this:
@import "main.css";
In this way, CSS can be hidden in IE4. Haha, it also saves 5 bytes. If you want to know the detailed explanation of @import syntax, you can see here "centricle's css filter chart"
16. Optimization for IE
Sometimes, you need to define some special rules for IE browser bugs. There are too many CSS techniques (hacks) here. I only use two of them. No matter what Microsoft is about to release Whether CSS is better supported in IE7 beta version, both methods are the safest.
1. Annotation method (a) hides a CSS definition in IE. You can use a child selector:
html>body p {
/* Definition content */
}
(b) The following writing method can only be understood by IE browser (hidden from other browsers)
* html p {
/* declarations */
}
(c) Sometimes, you want IE/Win to be active but IE/Mac to be hidden, you can use the "backslash" trick:
/* */
* html p {
declarations
}
/* */
2. Conditional comments method Another method, which I think is more testable than CSS Hacks, is to use Microsoft’s private attribute conditional comments (conditional comments). Using this method you can define some styles separately for IE without affecting the definition of the main style sheet. Like this:
<!--[if IE]>
<link rel="stylesheet" type="text/css" href="ie.css" />
<![endif]-->
17. Debugging skills: How big is the layer?
When debugging CSS errors, you have to be like a typewriter and analyze the CSS code line by line. I usually define a background color on the layer in question so it's obvious how much space the layer takes up. Some people suggest using border, which is generally possible, but the problem is that sometimes border will increase the size of elements, and border-top and boeder-bottom will destroy the vertical margin value, so it is safer to use background.
Another property that often causes problems is outline. Outline looks like boeder, but does not affect the size or position of the element. Only a few browsers support the outline attribute, the only ones I know of are Safari, OmniWeb, and Opera.
18. CSS code writing style When writing CSS code, everyone has their own writing habits for indentation, line breaks, and spaces. After constant practice, I decided to adopt the following writing style:
selector1,
selector2 {
property:value;
}
When using union definitions, I usually write each selector on its own line so they are easier to find in the CSS file. Add a space between the last selector and the curly braces {. Also write each definition on its own line. The semicolon should be placed directly after the attribute value. Do not add spaces.