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How to use CSS position property

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Mar 21, 2018 pm 04:22 PM

positionInstructions

This time I will bring you how to use the CSS position attribute. What are the precautions when using the CSS position attribute. Here is a practical case, let’s take a look.

At present, almost all mainstream browsers support the position attribute (except "inherit", "inherit" does not support all browsers including IE8 and previous versions of IE, and IE9 and IE10 have not been tested). The following is w3school Explanation of the five values of position:

Absolute and relative are the most commonly used, and fixed is also used more frequently (IE6 does not support fixed).

1. Absolute (Absolute positioning)

##Absolute is an element that generates visual positioning and is separated from the text flow. (That is, it no longer occupies a position in the document), refer to the upper left corner of the browser for positioning through top, right, bottom, left (TRBL for short). You can select a positioned parent object (the combination of relative and absolute will be discussed below) or the body coordinate origin for positioning, or you can perform hierarchical classification through z-index. When the TRBL value is not set, absolute uses the coordinates of the parent object as the starting point. When the TRBL value is set, the upper left corner of the browser is used as the original point. The specific case is as follows:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>position:absolute定位</title>
<style type="text/css">
    html,body,p{
                    margin:0;   
                    padding:0;  
                    list-style:none;
    }
    .center{
                margin:30px;
                border:#999999 solid 10px;
                width:400px;
                height:300px;
    }
    .p1{
            width:200px;
            height:200px;
            background:#0099FF;
            /*设定TRBL*/
            position:absolute;
            left:0px;
            top:0px;
    }
    .p2{
            width:400px;
            height:300px;
            font-size:30px;
            font-weight:bold;
            color:#fff;
            background:#FF0000;
    }
</style>
</head>
<body>
    <p class="center">
        <p class="p1"></p>
        <p class="p2">position:absolute定位测试</p>
    </p>
</body>
</html>

The effect of this code is as follows:

This is the effect after setting TRBL (setting TRBL uses the upper left corner of the browser as the origin). When TRBL is not set (when TRBL is not set, the coordinates of the parent object are used as the origin), change p1 to the following When coding

.p1{
            width:200px;
            height:200px;
            background:#0099FF;
            /*没有设定TRBL*/
            position:absolute;
    }

, the effect is as follows:

2. Relative (relative positioning)

relative means relative. As the name suggests, it means moving the element relative to the position where the element itself should appear in the document. , you can use TRBL to move the position of the element. In fact, the element still occupies the original position in the document, but it is visually moved relative to the original position. The specific case is as follows:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>position:relative定位</title>
<style type="text/css">
    html,body,p{
                    margin:0;   
                    padding:0;  
                    list-style:none;
    }
    .center{
                margin:30px;
                border:#999999 solid 10px;
                width:400px;
                height:300px;
                background:#FFFF00;
    }
    .p1{
            width:200px;
            height:150px;
            background:#0099FF;
            position:relative;
            top:-20px;
            left:0px;
    }
    .p2{
            width:400px;
            height:150px;
            font-size:30px;
            font-weight:bold;
            color:#fff;
            background:#FF0000;
    }
</style>
</head>
<body>
    <p class="center">
        <p class="p1"></p>
        <p class="p2">position:relative定位测试</p>
    </p>
</body>
</html>

The effect produced by the code is as follows:

3. The combination of relative and absolute

Floating is often used to layout the page during web design, but floating brings There are many uncertain factors (for example: IE browser compatibility issues). Relatively speaking, positioning in some layouts will be simpler, faster, and more compatible (used in combination with relative and absolute). The following is an example in a web page (the head part of the web page). The specific code is as follows :

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<style type="text/css">
html,body,p,ul,li,a{
                    margin:0;   
                    padding:0;  
                    list-style:none;
}
a, a:hover{
 color:#000;
 border:0;
 text-decoration:none;
}
    #warp,#head,#main,#foot
{
    width: 962px;
}
/*设置居中*/
#warp{
    margin: 0 auto;
}
#head{
            height:132px;
            position:relative;
}
.logo{
        position:absolute;
        top:17px;
}
.head_pic{
            position:absolute;
            top:17px;
            left:420px;
}
.sc{
            position:absolute;
            right:5px;
            top:12px;
}
.sc a{
            padding-left:20px;
            color:#666;
}
.nav{
        width:960px;
        height:42px;
        line-height:42px;
        position:absolute;
        bottom:0px;
        background:url(img/nav_bj.jpg) no-repeat center;
}
.nav ul{
            float:left;
            padding:0 10px;
}
.nav li{
            float:left;
            background:url(img/li_bj.jpg) no-repeat right center;
            padding-right:40px;
            padding-left:20px;
            text-align:center;
            display:inline;
}
.nav li a{
                font-size:14px;
                font-family:Microsoft YaHei !important;
                white-space:nowrap;
}
.nav li a:hover{
                    color:#FBECB7;
}
</style>
<title></title>
</head>
<body>
    <p id="warp">
        <p id="head">
            <p class="logo"><img  src="/static/imghwm/default1.png"  data-src="img/logo.jpg"  class="lazy"   / alt="How to use CSS position property" ></p>
            <p class="head_pic"><img  src="/static/imghwm/default1.png"  data-src="img/head_pic.jpg"  class="lazy"   / alt="How to use CSS position property" ></p>
            <p class="sc">
                <a href=""><img  src="/static/imghwm/default1.png"  data-src="img/sc_btn.jpg"  class="lazy"   / alt="How to use CSS position property" ></a>
                <a href=""><img  src="/static/imghwm/default1.png"  data-src="img/sy_btn.jpg"  class="lazy"   / alt="How to use CSS position property" ></a>
                <a href=""><img  src="/static/imghwm/default1.png"  data-src="img/kf_btn.jpg"  class="lazy"   / alt="How to use CSS position property" ></a>
            </p>
            <p class="nav">
                <ul>
                    <li><a href="">首页</a></li>
                    <li><a href="">关于我们</a></li>
                    <li><a href="">团队文化</a></li>
                    <li><a href="">公司动态</a></li>
                    <li><a href="">资讯参考</a></li>
                    <li><a href="">业务中心</a></li>
                    <li><a href="">合作银行</a></li>
                    <li><a href="">联系我们</a></li>
                </ul>
            </p>
        </p>
        <p id="main"></p>
        <p id="foot"></p>
    </p>
</body>
</html>

The effect is as follows:

In the above In the code, the relative positioning is first set for the head. Then you can see that all the child elements inside will be positioned relative to the head instead of relative to the body after setting absolute. This is much simpler and more convenient than using floating, and there is no need to worry about compatibility issues.

I believe you have mastered the method after reading the case in this article. For more exciting information, please pay attention to other related articles on the php Chinese website!

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