CSS Shadow Parts

In modern web development, CSS (Cascading Style Sheets) is an essential tool for styling and formatting web pages. One of the key features introduced in CSS for better styling control is Shadow Parts. CSS Shadow Parts allow developers to style parts of custom elements, enabling more flexibility and customization in web design.

Understanding Shadow DOM

Before diving into CSS Shadow Parts, it’s crucial to understand the concept of the Shadow DOM. Shadow DOM is a feature in web components that encapsulates the structure, style, and behavior of a custom element, keeping it separate from the rest of the document’s DOM. This encapsulation prevents styles from bleeding in or out of the custom element, ensuring better modularity and reusability.

What are CSS Shadow Parts?

CSS Shadow Parts extend the capabilities of Shadow DOM by allowing developers to define specific elements within a custom element that can be styled externally using regular CSS. These parts act as access points for styling, enabling developers to target and style specific components of a custom element without breaking encapsulation.

Basic Syntax of CSS Shadow Parts

To define CSS Shadow Parts, you need to use the ::part() pseudo-element selector followed by the name of the part you want to style. Here’s the basic syntax:

				
					:host::part(part-name) {
  /* Styles for the specified part */
}

In this syntax:

  • :host refers to the custom element itself.
  • ::part() is the pseudo-element selector for defining a shadow part.
  • part-name is the name of the part you want to style.

Creating Custom Elements with Shadow Parts

Let’s create a simple custom element with Shadow Parts to understand how they work.

				
					<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Custom Element with Shadow Parts</title><style>/* Define styles for the custom element */
    my-button::part(button) {
      background-color: #007bff;
      color: #fff;
      padding: 10px 20px;
      border: none;
      border-radius: 5px;
      cursor: pointer;
    }</style></head>
<body>
  
  <my-button>Click Me</my-button>

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</html>

In this example:

  • We’ve defined a custom element <my-button> with a Shadow DOM.
  • The ::part(button) selector styles the button part of the custom element.
  • Inside the JavaScript, we create a button element and append it to the Shadow DOM.

Advanced Usages of CSS Shadow Parts

Dynamic Styling

You can dynamically change the styles of shadow parts using JavaScript based on user interactions or application state. This allows for interactive and responsive styling of custom elements.

				
					<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Dynamic Styling with CSS Shadow Parts</title><style>/* Define styles for the custom element */
    my-button::part(button) {
      background-color: var(--button-bg-color, #007bff);
      color: var(--button-text-color, #fff);
      padding: 10px 20px;
      border: none;
      border-radius: 5px;
      cursor: pointer;
    }</style></head>
<body>
  
  <my-button id="dynamic-button">Click Me</my-button>

   <script type="litespeed/javascript">const button=document.getElementById('dynamic-button');button.addEventListener('mouseenter',()=>{button.style.setProperty('--button-bg-color','green');button.style.setProperty('--button-text-color','white')});button.addEventListener('mouseleave',()=>{button.style.removeProperty('--button-bg-color');button.style.removeProperty('--button-text-color')})</script> <script data-no-optimize="1">!function(t,e){"object"==typeof exports&&"undefined"!=typeof module?module.exports=e():"function"==typeof define&&define.amd?define(e):(t="undefined"!=typeof globalThis?globalThis:t||self).LazyLoad=e()}(this,function(){"use strict";function e(){return(e=Object.assign||function(t){for(var e=1;e<arguments.length;e++){var n,a=arguments[e];for(n in a)Object.prototype.hasOwnProperty.call(a,n)&&(t[n]=a[n])}return t}).apply(this,arguments)}function i(t){return e({},it,t)}function o(t,e){var n,a="LazyLoad::Initialized",i=new t(e);try{n=new CustomEvent(a,{detail:{instance:i}})}catch(t){(n=document.createEvent("CustomEvent")).initCustomEvent(a,!1,!1,{instance:i})}window.dispatchEvent(n)}function l(t,e){return t.getAttribute(gt+e)}function c(t){return l(t,bt)}function s(t,e){return function(t,e,n){e=gt+e;null!==n?t.setAttribute(e,n):t.removeAttribute(e)}(t,bt,e)}function r(t){return s(t,null),0}function u(t){return null===c(t)}function d(t){return c(t)===vt}function f(t,e,n,a){t&&(void 0===a?void 0===n?t(e):t(e,n):t(e,n,a))}function _(t,e){nt?t.classList.add(e):t.className+=(t.className?" 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In this example:

The button changes its background color to green and text color to white when hovered over.

We achieve this by dynamically setting CSS custom properties (--button-bg-color and --button-text-color) using JavaScript.

Multiple Shadow Parts

Custom elements can have multiple shadow parts, allowing for granular control over styling. Let’s create a custom element with multiple shadow parts: header and content.

				
					<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Custom Element with Multiple Shadow Parts</title><style>/* Define styles for the custom element */
    my-panel::part(header) {
      font-weight: bold;
      background-color: #007bff;
      color: #fff;
      padding: 10px;
    }

    my-panel::part(content) {
      padding: 20px;
      background-color: #f0f0f0;
    }</style></head>
<body>
  
  <my-panel>
    <div slot="header">Header</div>
    <div slot="content">Content</div>
  </my-panel>

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            /* Styles for the custom element */
            :host {
              display: block;
              border: 1px solid #ccc;
              border-radius: 5px;
              margin: 20px;
            }
          </style>
          <div part="header"><slot name="header"></slot></div>
          <div part="content"><slot name="content"></slot></div>
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</html>

In this example:

We define two shadow parts, header, and content, using the ::part() pseudo-element selector.

The custom element <my-panel> contains a header and content slots for inserting content.

Each part is styled separately, allowing for different styles for the header and content sections of the custom element.

Inheritance

Shadow parts can inherit styles from parent elements, making it easier to maintain consistent styling across an application. Let’s demonstrate this with an example where a parent element’s styles are inherited by its child custom element.

				
					<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Inheritance with CSS Shadow Parts</title><style>/* Styles for the parent element */
    .container::part(button) {
      background-color: #007bff;
      color: #fff;
      padding: 10px 20px;
      border: none;
      border-radius: 5px;
      cursor: pointer;
    }</style></head>
<body>
  
  <div class="container">
    
    <my-button>Inherited Button</my-button>
  </div>

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</html>

In this example:

The parent element .container defines a shadow part for styling buttons.

The custom element <my-button> is placed inside the parent element, inheriting the button styles defined for the container.

CSS Shadow Parts are a powerful feature in modern web development, providing developers with the ability to style specific parts of custom elements while maintaining encapsulation and modularity. By leveraging CSS Shadow Parts, developers can create highly customizable and reusable web components, enhancing the overall user experience of web applications. Happy Coding! ❤️

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