Detailed explanation on CSS3 multiple backgrounds and background image cropping, positioning and size

黄舟

Release： 2017-05-21 16:34:01

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Before CSS3 we could add a image to the background

CSS3 allowed us to add multiple images to one element

Multiple background images

<p class="demo"></p>

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.demo {    width: 600px;    height: 200px;    border: 1px solid black;    background: url(&#39;1.png&#39;) no-repeat;}

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Multiple backgrounds You can add multiple image resources to the background attribute, separate them with commas
and then use background -position Position them where you want

.demo {    width: 600px;    height: 200px;    border: 1px solid black;    background: url(&#39;1.png&#39;) no-repeat,                url(&#39;2.png&#39;) no-repeat 200px 0,                url(&#39;3.png&#39;) no-repeat 400px 0;}

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If no-repeat is not set, the image resources below will overwrite the image resources above

Pictures Starting positionbackground-origin

background-origin allows us to define where the image starts to be positioned
optional attribute valuepadding-box (default), border-box, content-box;
padding-box default image starts from padding
We can add padding to prove this

.demo {    width: 600px;    height: 200px;    border: 20px solid gray/*改*/;    padding: 20px/*增*/;    background: url(&#39;1.png&#39;) no-repeat,                url(&#39;2.png&#39;) no-repeat 200px 0,                url(&#39;3.png&#39;) no-repeat 400px 0;}

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[Note: Comments cannot be used in css. I am commenting like this for the purpose of highlighting. Don’t be misled]

border-box defines the image starting from the border

.demo {    width: 600px;    height: 200px;    border: 20px solid gray;    padding: 20px;    background: url(&#39;1.png&#39;) no-repeat,                url(&#39;2.png&#39;) no-repeat 200px 0,                url(&#39;3.png&#39;) no-repeat 400px 0;    background-origin: border-box/*增*/;}

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After changing to border-box, we found that part of the image was blocked at the bottom of the gray background color
It can be understood that the border should actually be above the element

.demo {    width: 600px;    height: 200px;    border: 20px solid gray;    padding: 20px;    background: url(&#39;1.png&#39;) no-repeat,                url(&#39;2.png&#39;) no-repeat 200px 0,                url(&#39;3.png&#39;) no-repeat 400px 0;    background-origin: content-box/*改*/;}

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content-box defines the starting position from the content part of the element

Picture croppingbackground-clip

Although we The starting position is set to the content area
But this does not mean that our picture is limited to the content area
It can be drawn within the entire element border and within the border
You can slightly modify the above code to prove This

.demo {    width: 600px;    height: 200px;    border: 20px solid transparent/*改*/;    padding: 20px;    background: url(&#39;1.png&#39;) no-repeat,                url(&#39;2.png&#39;) no-repeat 200px 0,                url(&#39;3.png&#39;)/*删掉no-repeat 默认repeat*/ 400px 0;    background-origin: content-box;}

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So is there a way to set the range of image display?
This uses our background-clip attribute
and content-origin attributes The values are similar
There are padding-box (default), border-box, content-box;
Set the image display range, as if it has been cropped

.demo {    width: 600px;    height: 200px;    border: 20px solid transparent;    padding: 20px;    background: url(&#39;1.png&#39;) no-repeat,                url(&#39;2.png&#39;) no-repeat 200px 0,                url(&#39;3.png&#39;) 400px 0;    background-origin: content-box;    background-clip: content-box/*增*/;}

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In this way, the excess part of the image will not be visible.

The image cropping attribute in our webkit also has a special attribute value which is text
It means that the background image is limited to the text
Combined with text-fill-color, a unique masking text effect can be formed. Learn about

<p class="demo">某科学的超电磁炮</p>  <--添加内容

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.demo {    width: 600px;    height: 200px;    border: 20px solid transparent;    padding: 20px;    background: url(&#39;1.png&#39;) no-repeat,                url(&#39;2.png&#39;) no-repeat 200px 0,                url(&#39;3.png&#39;) 400px 0;    background-origin: content-box;    -webkit-background-clip: text;/*增*/
    -webkit-text-fill-color: transparent;/*增*/
    font: 75px/200px bold;/*增*/}

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##Picture size

background-size

Back to one of our pictures

Background-size This attribute allows us to control the size of the picture
For example, write two pixel values to control the width and height

.demo {/*新*/
    width: 600px;    height: 200px;    border: 1px solid black;    background: url(&#39;1.png&#39;) no-repeat;    background-size: 180px 140px;}

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Write one pixel The value means that the width and height are the same in pixels
Of course it can also be written in percentage form

In addition, there are two keywords: cover and contain

cover covers the entire area. In our example, the width will be full

.demo {    width: 600px;    height: 200px;    border: 1px solid black;    background: url(&#39;1.png&#39;) no-repeat;    background-size: cover/*改*/;}

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contain is to ensure that the image is displayed at its maximum within the area, and in our example the height will be full

.demo {    width: 600px;    height: 200px;    border: 1px solid black;    background: url(&#39;1.png&#39;) no-repeat;    background-size: contain;}

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