How to set css scope

In CSS, you can use the scoped attribute to set the scope; when the style tag has the scoped attribute, its CSS only affects the elements in the current component. However, the root node of a child component will be affected by both its parent-scoped CSS and the child component's scoped CSS.

The operating environment of this tutorial: Windows 7 system, CSS3&&HTML5 version, Dell G3 computer.

When I first came into contact with Vue single file, I was a little confused about the scoped attribute in the style tag. After all, I have never used it before. Here are some explanations about scoped.

A standard .vue file looks like this:

// html内容区域
<template>
  <div class="hello">
    <h1>{{ msg }}</h1>
  </div>
</template>

//相关数据及事件区域，通俗说就是我们写JS代码的地方
<script>
export default {
  name: &#39;HelloWorld&#39;,
  data () {
    return {
      msg: &#39;Welcome to Your Vue.js App&#39;
    }
  }
}
</script>

// CSS样式区域
<!-- Add "scoped" attribute to limit CSS to this component only -->
<style scoped>
    .hello { color: #efefef; }
</style>

You can see that there is a scoped attribute in the style tag. When the style tag has a scoped attribute, its CSS only acts on the current elements in the component. This is similar to style encapsulation in shadow DOM. It has some caveats, but does not require any profill. It achieves the following transformation by using PostCSS:

<style scoped>
.example {
  color: red;
}
</style>

<template>
  <div class="example">hi</div>
</template>

Conversion result:

<style>
.example[data-v-f3f3eg9] {
  color: red;
}
</style>

<template>
  <div class="example" data-v-f3f3eg9>hi</div>
</template>

Mixing local and global styles

There is one thing worth noting, in You can use both scoped and unscoped styles in a component:

<style>
/* 全局样式 */
</style>

<style scoped>
/* 本地样式 */
</style>

The child element style is the result of the interaction between the root element of the child element and the CSS within the child component

After using scoped, the styles of the parent scope will not penetrate into the child components. However, the root node of a child component will be affected by both its parent-scoped CSS and the child component's scoped CSS. This design is to allow the parent component to adjust the style of the root element of its child component from a layout perspective. The example is as follows:

child component

<template>
    <div class="wrap">
        <p>Hello world</p>
    </div>
</template>

<style scoped>
    .wrap {
        color: #ffffff;
        background: #666666;
    }
</style>

parent component

<template>
    <div class="wrap">
       //ChildMOdul为上面的子组件 
       <ChildModul/>
    </div>
</tamplate>
<style scoped>
//子组件根元素样式
    .wrap {
        margin: 0 10px
    }
</style>

A style with a background color of #efefef and a color of #ccc is defined in the child component. In the parent element, a 10px border is defined for the root element of the child component. The final style displayed by the child module is as follows:

As can be seen from the above figure, the style of the sub-component is the result of the joint action of the root element of the sub-component in the parent component and the scoped CSS style in the sub-component.

Depth-acting selector

If you want a selector in a scoped style to act "deeper", such as affecting child components, you can use>> ;>Operator:

<style scoped>
.a >>> .b { /* ... */ }
</style>

The above code will be compiled into:

.a[data-v-f3f3eg9] .b { /* ... */ }

Some preprocessors like Sass cannot parse correctly>>>. In this case you can use the /deep/ operator instead – this is an alias for >>> and will work just as well. Try using the previous code and use the depth action selector to set the style of the child component in the parent component:

Parent component

.wrap /deep/ .child--css {
    font-size: 36px;
  }

Rendering:

You can see from the height that the style has been applied to the subcomponent. I know you may want to ask why you use /deep/ instead of >>> if you don’t see the Sass preselector. I actually don’t know this. I used >>> first and it didn’t work. Then I switched to /deep/ and the style was effective. To be irresponsible, if >>> doesn't work, just change it to /deep/. Anyway, the purpose is to allow the styles written in the parent component to penetrate into the child components. . .

Dynamically generated content

DOM content created through v-html is not affected by styles within the scope. But you can still style them via deep action selectors.

Need to pay attention to events

• CSS scope cannot replace class: Considering that the browser renders various CSS selectors way, when p{ color: red } is scoped (i.e. when used in combination with attribute selectors) it will be many times slower. If you use class or id instead, such as .example { color: red }, the performance impact will be eliminated.

• Use descendant selectors carefully in recursive componentsFor CSS rules in selector .a .b, if the element matching .a contains a recursive subcomponent, then .b in all subcomponents will be matched by this rule.

Recommended learning: css video tutorial

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