Attach a class 2

App.xht

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

<Button .btn="red bold" name="Red bold" />
<Button .btn="purple" name="Purple" />
<Button name="Default" />

<style>
    .red {color: red;}
    .purple {color: purple;}
    .bold {font-weight: bold;}
</style>

Button.xht

<script>
    export let name;
</script>

<button class="btn">{name}</button>

<style>
    .btn {font-style: italic;}
    :export(.btn) {color: deepskyblue;}
</style>