HTML Exportparts for Forwarded Component Styling

Let’s take one interactive feature apart so the markup and behavior make sense separately.

What You Need to Know

Exportparts forwards selected parts through another shadow boundary. Without it, a page's CSS cannot necessarily reach the named part inside a nested component.

Try the Example

Take a look at the example. We’ll explain the important lines right below it.

<student-card exportparts="heading: card-heading">
    <template shadowrootmode="open">
        <h2 part="heading">Student card</h2>
        <slot></slot>
    </template>
    <p>Student: Alex</p>
</student-card>
<style>student-card::part(card-heading) { font-weight: bold; }</style>

Let’s Read the Code

part: Part exposes selected pieces of a shadow tree for outside CSS styling.
<template>: A template stores markup that is inactive until it is cloned or used as declarative shadow content.
<h2>: A heading divides the page into understandable parts.
exportparts: Exportparts forwards part names through a nested component.

Read the named elements and attributes together. They explain how the browser connects this feature to the rest of the page.

What Happens in the Browser?

When this example includes JavaScript, it supplies behavior that ordinary HTML does not automatically provide. Always think about a fallback.

Start with native behavior. Details, dialog, and popover each solve a different interface problem. Choose the simplest control that actually matches what a visitor wants to do, then test focus and dismissal as well as appearance.

Your Turn

Run this on a local development server if it loads modules or resources. Change the visible text or trigger and check what still works with scripts disabled.

Common Beginner Mistakes

Assuming new HTML syntax works in every browser without testing.
HTML supplies structure; JavaScript is necessary for the scripted behavior in this example. Check keyboard access and focus movement too.

Key Takeaways

Exportparts forwards selected parts through another shadow boundary.
part: Part exposes selected pieces of a shadow tree for outside CSS styling.
Test the behavior you expect rather than trusting how the snippet looks in your editor.