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This article mainly introduces the relevant information on using css3+ pseudo-elements to achieve the effect of underlines expanding to both sides when the mouse is moved in. The article first gives a detailed introduction to facilitate everyone's understanding, and then provides a complete example code for everyone to refer to and learn. Friends who need it, please come and study together. Hope it helps.
Let’s take a look at the renderings first:
Implementation ideas:
Combine pseudo elements: before and: After is positioned in the middle of the bottom of the element and sets the width from 0 to 100% to achieve the goal.
Implementation method:
1. First define a block element (inline elements have no width and height) and modify the style to a rectangle with a light gray background color, and set relative positioning.
html code
css style
#underline{
width: 200px;
height: 50px;
background: #ddd;
margin: 20px;
position: relative;
}
2. Set two pseudo elements: before and :after, and set them to have a background color of blue (that is, underline color), use absolute positioning to fix the two elements to the bottom middle position of #underline.
css style
#underline:before,
#underline:after{
content: "";/*单引号双引号都可以，但必须是英文*/
width: 0;
height: 3px; /*下划线高度*/
background: blue; /*下划线颜色*/
position: absolute;
top: 100%;
left: 50%;
transition: all .8s ; /*css动画效果，0.8秒完成*/
}
3. Set the mouse move-in effect.
css style
#underline:hover:before{/*动画效果是从中间向左延伸至50%的宽度*/
left:0%;
width:50%;
}
#underline:hover:after{/*动画效果是从中间向右延伸至50%的宽度*/
left: 50%; /*这句多余，主要是为了对照*/
width: 50%;
}
Optimization
1. Although the purpose was achieved, two pseudo-elements were used, one extending 50% to the left and the other 50% to the right. , can only one extension to 100% achieve the goal?
css code
#underline:after{
content: "";
width: 0;
height: 5px;
background: blue;
position: absolute;
top: 100%;
left: 50%;
transition: all .8s;
}
#underline:hover:after{/*原理是left:50%变成0%的同时，宽度从0%变成100%*/
left: 0%;
width: 100%;
}
2. Only define the :after pseudo-element, and change it from 50% to the left with a width of 0 to 0% from the left with a width of 100%. It can be implemented, thereby achieving the purpose of streamlining the code, and adding :before to facilitate other operations.
Complete code
鼠标移入下划线展开
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