Is possible to style parent from child with scoped?

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05-10-2024

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Can You Style a Parent from a Child with Scoped CSS in Vue?

In Vue.js, scoped CSS is a powerful tool for keeping your styles isolated within individual components. But what happens when you want to style an element in a parent component based on the state of a child component?

Let's explore this common question with a practical example.

The Problem: Styling a Parent Based on Child State

Imagine you have a simple button component and a parent component displaying a list of items. You want the parent container to have a different background color depending on whether the button is currently active or not.

Parent Component (Parent.vue):

<template>
  <div class="container">
    <p>List of Items:</p>
    <ul>
      <li v-for="(item, index) in items" :key="index">
        {{ item }}
      </li>
    </ul>
    <Button :active="isActive" @click="toggleActive" />
  </div>
</template>

<script>
import Button from './Button.vue';

export default {
  components: {
    Button,
  },
  data() {
    return {
      items: ['Item 1', 'Item 2', 'Item 3'],
      isActive: false,
    };
  },
  methods: {
    toggleActive() {
      this.isActive = !this.isActive;
    },
  },
};
</script>

<style scoped>
.container {
  background-color: #f0f0f0;
  padding: 20px;
}
</style>

Child Component (Button.vue):

<template>
  <button :class="{ active: active }">
    Click Me
  </button>
</template>

<script>
export default {
  props: {
    active: Boolean,
  },
};
</script>

<style scoped>
.active {
  background-color: #4CAF50;
  color: white;
}
</style>

Here, the active class is applied to the button element when the active prop is true. But we can't directly style the parent container using this class. The scoped attribute in our CSS confines styles to the current component, preventing them from affecting elements outside its boundaries.

The Solution: CSS Variables and Communication

There are a few ways to overcome this limitation. The most elegant approach is to use CSS variables (custom properties) in combination with prop passing:

1. Define a CSS variable in the parent component:

   <style scoped>
   .container {
     background-color: #f0f0f0;
     padding: 20px;
     background-color: var(--container-bg);
   }
   </style>
   

2. Pass the variable value to the child component:

   <Button :active="isActive" @click="toggleActive" :containerBg="isActive ? '#4CAF50' : '#f0f0f0'" />
   

3. Use the variable in the child component's CSS:

   <style scoped>
   .active {
     background-color: #4CAF50;
     color: white;
   }
   
   .active::before {
     content: '';
     display: block;
     position: absolute;
     top: 0;
     left: 0;
     right: 0;
     bottom: 0;
     z-index: -1;
     background-color: var(--container-bg);
   }
   </style>
   

In this revised code:

• The parent component defines a CSS variable --container-bg for its background color.
• The child component receives this variable value through the containerBg prop.
• The child component uses ::before pseudo-element to create a background layer that inherits the --container-bg value.

This technique ensures that the container background color changes when the button's active state changes. The ::before pseudo-element allows us to target the container from within the child component's scope without breaking encapsulation.

Conclusion: Scoped CSS Doesn't Limit Creativity

While scoped CSS provides isolation, it doesn't restrict you from creatively influencing the styles of parent components. By using CSS variables and communication between components, we can achieve a visually responsive layout while maintaining modularity and code organization.

This approach is widely applicable for building more complex interfaces, where elements can interact with each other based on dynamic state changes.

Remember: CSS variables and communication are powerful tools for controlling styles within your Vue.js components, offering a flexible and scalable way to create interactive and visually engaging user experiences.