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Created September 26, 2015 06:51
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css.md

CSS Tricks

教材：http://www.codeschool.com/courses/css-cross-country

Style 生效的位置

  • inline style
  • 在 <head> </head> 裡面
  • external link: 如 link rel="stylesheet" href="style.css"

CSS Selectos

  • Element selector
  • Class selector
  • ID selector
  • Compound selector : h1#header

Advanced Selector

ref: Taming Advanced CSS Selectors

  • #sidebar h2 — 0, 1, 0, 1
  • h2.title — 0, 0, 1, 1
  • h2 + p — 0, 0, 0, 2
  • #sidebar p:first-line — 0, 1, 0, 2

cascade order

優先權照

  • external <link>
  • <head>
  • inline style
  • !important
  • 相同的 selector 重複的屬性，後寫的會覆蓋前面的。沒有重複的則會合併。

Float

定義

  • 把元素從傳統的 document flow 中移除，然後浮動掛在指定的邊界上。
  • 其他在 parent 元素的內容會繞著這個 float 的元素排列。

種類

  • float: left
  • float: right
  • float: none

Stacking order

  • 浮動的元素從 parent 的左/右邊界開始排，不夠放的話會找另下一個可以停泊的邊界繼續排
  • 如果浮動的元素高度不同，例如左邊的特別長，旁邊的元素的比他短，則下一個停泊的不會是左邊界，而是會停在左邊元素的右邊。（下一個可以停泊的邊界原則）

floating left & right

同時使用 float:left 與 float:right，寬度夠的話，會分列兩邊。如果寬度不夠，以先 claim 的會是第一排(靠右），後 claim 的會被扔到下一排（靠左）去。

<div>
<div class="content1"> </div>
<div class="content2"> </div>
</div>
.content1 {
float:right;
}
.content2 {
float:left;
}

clearfix

為什麼要使用 cleafix

  • 狀況一：float 元素可能比旁邊的非 float 元素高。（因為 float 沒有高度）所以下一段會黏上來。
  • 狀況二：所有的 children 都是 float。（因為 float 沒有高度）所以 container 看起來會太短。
常用 clearfix 技巧
clear with a subsequent elemet ( 在下面的元素放 clear: both )
  • 但這一招移動 div 順序就會爆炸
  • 背景和邊界不會被展延

失敗！

manual clearing （手動在下面塞一個空的 div，對它下 clear: both)
  • 需要塞一個空的 element
  • 看起來很礙眼

正解技巧 ( self-cleared )

.group:before, .group:after { 
content: "";
display: table; 
}
.group:after {
clear: both; 
}
.group { 
zoom: 1; /* IE6&7 */ 
}
.group 要下在 parent node
<div class="group">
<div class="float-left"> </div>
<p> blah </p>
</div>

Inheritance & Specificity

  • 巢狀元素會自動繼承 parent 的 style
  • 可以 override parent 的 style
  • id 比 class 的優先權高

優先權算法

0,0,0,0

  • 第一個數字：inline style
  • 第二個數字：of ID selectors
  • 第三個數字：of class selectors
  • 第四個數字：of element seletors
example
  • p { color: #fff; } # 0,0,0,1
  • .intro { color: #98c7d4; } # 0,0,1,0
  • #header { color: #444245; } # 0,1,0,0
  • <h1 style="color: #000;">Mogul</h1> # 1,0,0,0
  • p { color: #fff !important; }

越大的可以把祖先蓋掉。

延伸閱讀：Don’t use ID selectors in CSS

box model

由內往外是

  • content area
  • padding area
  • border area
  • margin area

寬度計算

box width = content width + padding width + border width

overflow

  • visible: the default value, which allows content to extend beyond container boundaries
  • auto: adds a scrollbar as needed when content overflows
  • hidden: hides content that extends beyond the container
  • scroll: adds a scrollbar at all times, even if unneeded

positioning

有四種

  • static
  • relative
  • absolute
  • fixed

定義

  • Elements have a position value of static by default
  • Using a value other than static causes an object to become a positioned element
  • Positioned elements may use the top, left, bottom, and right properties for placement

Relative positioning

Renders in the normal flow, then shifted via positioning properties

Absolute positioning

Takes an element out of the normal flow for manual positioning

定位技巧

parent element 下 relative，內部需要定位的元素下 absolute，就不會超過邊界。

Fixed positioning

Affixes an element to a specific place in the window, where it will stay regardless of scrolling。（在螢幕上永遠保持不動，釘住）

z-index

  • No z-index or equal z-index = overlap determined by placement in DOM （後放的疊在先放的上面）
  • Higher values appear above lower values（ z-index 比較大的在比較上面）
  • Elements must be positioned for z-index to take effect. Use relative if you're not interested in moving the object （必須先被「定位」，才能使用 z-index)

延伸閱讀： Understanding CSS z-index

整理 CSS code

用 ,

p .content h3{
color: red;
}

padding/margin 上右下左

.content {
margin: 15px 10px 0 20px; /* top right bottom left */ }
}

其他綜合

font: 16px/18px bold italic sans-serif; /* size/line-height weight style family */
background: #000 url(image.jpg) no-repeat center top; /* color image repeat x-pos y-pos */
list-style: disc inside none; /* style position image */
margin or padding: 0 10px 0 10px / 0 10px 0 / 0 10px; /* top right bottom left / top right&left bottom / top&bottom right&left */
border: 3px solid #ccc; /* width style color */

Display types

block

  • Stretch the full width of their container ( container 有多寬就延伸到多寬)
  • Behave as though there is a line break before and after the element （有斷行效果）
  • Full box model can be manipulatedDisplay Types

Block elements: Tags that are block-level by default: <div>, <p>, <ul>, <ol>, <li> and <h1> through <h6>.

inline

  • Typically found within block-level elemeiner 有多寬就延伸到多寬)
  • Behave as though there is a line brethe content inside （只有內容的寬度）
  • Do not generate a line break before and after the content （沒有斷行效果）

Tags that are inline by default include <span>, <a>, <em>, <img>

inline-block

  • Same flow as an inline element but behave as a block element (可以玩 box model)

水平置中技巧

Centering a block-level element

  • Define a width, and the element width must be less than that of the parent container
  • margin: 0 auto;

Centering inline and inline-block elements

  • text-align: center

margin 重疊問題

多個 margin 疊在一起，會有 margin 重疊問題（ margin 會合併計算，取最大的。假設第一個 div margin-bottom: 40px，第二個 div margin-top: 20px。則他們的距離æmeiner 有多寬就延伸到多寬)

  • Behave as though there is a line brethe content inside （只有one or more block element has:

  • Padding or border

  • Relative or abs容的寬度）

  • Do not generate a line break before and after the content （沒有斷行效果）

Tag2/ontent （沒有斷行效果）

Tags that are inline by default ines### inline-block

  • Same flow as an inline element but behave as a block element (可以玩 box model)

##/)

Content Image 與 Layout image

  • Content should be markewidth, and the element width must be less than that of the parent container
  • margin: 0 auto;

Centerimlner

  • margin: 0 auto;

Centering inline and inline-block elements


``` css
crop {
height: 300px; 
width: 400px; 
overflow: hidden;
}
.crop img {
height: 300px; 
margin 會合併計算，取最大的。假設第一個 div margin-botïx。則他們的距離æmeiner 有多寬就延伸到多寬)
* Behave as though there is a line brethe conteimage-uploading instructions in your CMS

延伸閱讀：[Experiments with wide images](http://clagnut.com/sandbox/imagetest)

<hr>

### 圖片取代文字技巧

使用 text-indentand after the content （沒有斷行效果）

Tag2/ontent （沒有ædefault ines### inline-block

* Same flow as an inline element but behave as a block element (可以玩 box ç markewidth, and the element width must be less than that of the parent container
* margin: 0 auto;

### Centerimlner
* margin: 0 auto;

### Centering inline and inline-block elem）

Advantages to the sprite approach:

* Reduces number of HTTP image requests 
* Removes loading flash / need for preload


#### 使用方法

Multiple images & states:

.twitter, .github { background: url(social.png); display: block; height: 100px; width: 100px; text-indent: -9999px; } .github { background-position: -100px 0; } .twitter:hover, .twitter:focus { background-position: 0 -100px; } .github:hover, .github:focus { background-position: -100px -100px; }


延伸閱讀: [Spritecow](http://w£文字技巧

使用 text-indentand after the content （沒有斷行æet ines### inline-block

* Same flow as an inline element but behave as a block element (可以玩 box ç mardolock element (可以玩 box ç markewidth, and the element width must bRe
* margin: 0 auto;

### Centerimlner
* margin: 0 auto;

### Centering inline and inline-block elem）

Advanta
<ine and inline-block elem）

Advantages to the sprite approach:

* Redommoves loading flash / need for preload


#### 使用方法

Multiple images & states:

.twitter, .githu` es & states:

.twitter, .github {
background: url(social.pngml
<blockquote>
Coffee? Hah! Our cocoa is far better.
<span></span>
</blockquote>

原本是對 blockquote span 下 styling。

改成對 blockquote:before 下 styling。

html 可以砍成

<blockquote>
Coffee? Hah! Our cocoa is far better.
</blockquote>

利用 before, after 實作縮排

延伸閱讀：A Whole Bunch of Amazing Stuff Pseudo Elements Can Do

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