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This article mainly explains "what are the common optimization techniques of DIV CSS". Interested friends may wish to have a look. The method introduced in this paper is simple, fast and practical. Next, let the editor take you to learn "what are the common optimization skills of DIV CSS?"

one。 Use css abbreviations

Using abbreviations can help reduce the size of your CSS file and make it easier to read.

two。 Ming Ken said that the unit, unless the value is 0

Forgetfulness says that the unit of size is a common mistake made by CSS veterans. In HTML you can only write width=100, but in CSS, you have to give an exact unit, such as width:100px width:100em. There are only two exception situations that can be undefined: the row height and the 0 value. In addition, other values must follow units, so be careful not to add spaces between values and units.

three。 Distinguish case from case

When using the elements defined in CSS,CSS in XHTML, it is commonly known as overwriting. In order to combat this mistake, I advocate that all definitions should be capitalized.

The values of class and id are also very different in HTML and XHTML. If you do not necessarily need to overwrite, please bear the responsibility to make sure that your definition in CSS is consistent with the tag in XHTML.

four。 Unqualify elements before class and id

When you write an element definition class or outline id, you can omit the previous element constraints, because ID is unique on a page, class can be used frequently on the page. You limit a certain element. For example:

Div#content {/ * declarations * /} fieldset.details {/ * declarations * /}

It can be written as

# content {/ * declarations * /} .details {/ * declarations * /}

How you can throw away some bytes.

five。 Default value

Usually, the default value of padding is 0, and the default value of color is transparent. However, the default values of different browsers may be different. If you are afraid of argument, you can define all elements with margin and padding values of 0 at the end of the stylesheet, like this:

* {margin:0; padding:0;}

six。 You don't need to define the inheritable value several times.

In CSS, child elements actively inherit the attribute values of the parent element, such as color, font, etc., which have been defined in the parent element, can be inherited directly in the child element, there is no need to say again and again. Note, however, that browsers may override your definition with some default values.

seven。 Principle of nearest priority

Assume that there are multiple definitions of competing elements, with the definition of the most imminent (minimum level) as the top priority, for example, if there is such a piece of code

Update: Lorem ipsum dolor set

In the CSS file, you also defined the element p and a classupdate

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.

eight。 Multiple class theory

A tag can define multiple class at the same time. For example, let's first define two formats, the first with a background of # 666 and the second with a border of 10 px.

.one {width:200px;background:#666;} .two {border:10px solid # F00;}

In the page code, we can call

What a final revelation is that this div has the backing of # 666 and the frame of 10px. Yes, it's OK to do that. You can try it.

nine。 Use a sub-selector (descendant selectors)

CSS beginners do not know that the use of sub-selectors is one of the notices that affect their compliance. The sub-selector can help you save a little bit of class definition. Let's look at the following code:

Item 1 > Item 1 Item 1

The CSS definition of 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 use the following method to cover the following code

Item 1 Item 1 Item 1

The name circle says that it is:

# subnav {/ * Some styling * /} # subnav li {/ * Some styling * /} # subnav a {/ * Some styling * /} # subnav .sel {/ * Some styling * /} # subnav .sel {/ * Some styling * /}

Using sub-selectors can make your code and CSS more concise and easier to read.

ten。 It's not important to put quotation marks on the road of the set picture.

In order to save bytes, I suggest not to add quotation marks to the background picture ladder, because quotation marks are not necessary. For example:

Bac kg round:url (images/***.gif) # 333

Can be written as

Background:url (images/***.gif) # 333

If you add quotation marks, it will cause some mistakes in the reader.

eleven。 Group selector (Group selectors)

When some element types, class or id all have attributes together, you can use the group selector to prevent repeated statements. This can waste a lot of bytes.

For example: define the font, color and margin of all the title questions, how much you can write:

H _ 2 font-family:Lucida Grande,Lucida,Arial,Helvetica,sans-serif; color:#333; margin:1em h 3, h 4, h 5, h 6, h 7 {font-family:Lucida Grande,Lucida,Arial,Helvetica,sans-serif; color:#333; margin:1em 0;}

If there is an independent definition of individual element requirements in the duration, you can add a new definition, which can cover the old definition, for example:

H2 {font-size:2em} h3 {font-size:1.6em}

twelve。 Specify the pattern of the link at the correct pace

When you use CSS to define multiple shape styles of a link, pay attention to the order in which they are copied. The correct procedure is: link: visited: hover: active. The first letter extracted is LVHA, and you can imagine it as LoVe HAte (LOVE hate). Why is it that reference can be made to Eric Meyer's "Link Specificity"?

If your users are important to use the keyboard to discipline, you need to know the center of the current link, you can also define: focus attribute. The achievement of the focus attribute also depends on the status of your transcription. if you expect the focus element to reflect: hover attainments, you write: focus in front of: hover; assuming that you hope to focus results instead of: hover effect, you put: focus after: hover.

thirteen。 Eliminate floating

A non-constant CSS problem, when floating is used, the lower layer is covered by the floating layer, and the sublayers nested in the outline layer are beyond the scope of the outer layer.

The usual solution is to add an extra element in front of the floating layer, such as a div or a br, not to mention that it is defined as clear: both. This door path is a little far-fetched, happiness is that there is still a good way to covet.

The above two methods can be very delusional about the problem of floating high, but what if you really need to clear the layer or the objects in the layer? A simple method is equivalent to using the overflow attribute.

Which of the following clear methods is more appropriate for you, depending on the specific environment, I won't talk about it here.

fourteen。 Horizontal Center (centering)

It's an easy strategy, but it's worth repeating, because I've seen too many expert questions asking this: how does CSS center horizontally? You important define the width of the element, and define the horizontal margin, if your layout is included in a layer (container), like how:

How can you define how to center it horizontally:

# wrap {width:760px; / * modified to the width of your layer * / margin:0 auto;}

However, IE5/Win cannot present this definition correctly, and we take a very useful talent to manage it: using the text-align attribute. It's like this:

Body {text-align:center;} # wrap {width:760px; / * modified 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 body in IE5/Win are centered (other browsers just center pen and ink), and the second text-align:left; places text in # warp to the left.

fifteen。 Import (Import) and latent CSS

Because the old version of Wade Hunter didn't approve of CSS, a common practice is to use @ import to lurk CSS. For example:

@ import url (main.css)

However, this method can not afford to infect IE4, which gave me a headache for a while. And then I wrote it like this:

@ import main.css

How can also ambush CSS in IE4, ha ha, but also extravagant 5 bytes.

sixteen。 Optimization for IE

Sometimes, you need to define some special rules for the flaws of IE readers. There are too many CSS skills (hacks). I only use two of these methods, regardless of whether Microsoft is better in favor of CSS in the upcoming IE7 beta version. These two methods are usually the safest.

1. The method of dredging

(a) lurking a CSS interface in IE, you can use a sub-selector (child sele CTO r):

Html > body p {/ * define schema * /}

(B) the following writing can only be understood by IE browsers (hidden from other browsers)

* html p {/ * declarations * /}

(C) there are other times when you want IE/Win to be effective and IE/Mac is hidden, you can use backslash:

/ * html p {declarations} / * * /

two。 The method of premise expression (conditional co sister ents)

Another approach, which I think is more honed than CSS Hacks, is to adopt Microsoft's conditional comments. In this way, you can define individual entries for IE without affecting the definition of the main name table. It's like this:

seventeen。 Debugging ability: how big is the layer?

When an error occurs in debugging CSS, you have to synthesize the CSS code line by line, like a typesetter. I usually define a backing color on the layer where something goes wrong, so I can clearly see how much space the layer conquers. Some people advocate the use of border, but the problem is that sometimes border will increase the size of elements, border-top and boeder-bottom will break the vertical margin value, so it is more secure to use background.

Another attribute that often goes wrong is outline. Outline looks like boeder, but does not affect the size or approximate position of the element. As long as most dabblers approve of the outline attribute, all I know is Safari, OmniWeb, and Opera.

XVIII. CSS code writing style

When writing CSS code, each group has its own writing folklore for indentation, line breaks, and spaces. After continuous practice, I decided to adopt the following copying style:

Selector1, sele CTO R2 {property:value;}

When using decentralized definitions, I usually write a separate line for each selector, and I find them in the CSS file. Add a space between the last selector and the curly braces {, write a single line for each definition, and the semicolon directly after the attribute value, do not add a space.

I still like to add a semicolon on the reverse side of each attribute value, although the rule allows the negative side of the last attribute value not to write a semicolon, but if you want to add a new pattern, it is easy to forget to add the semicolon and give rise to errors, so it is better to add it all the same.

At the end, the closed curly braces} write a single line.

Spaces and line breaks help with reading.

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