how to listen for event in child component update parent UI Astro file client side

I have a Parent Astro page, where i have a svelete component.i wanna Update some UI on the parent astro page when a button gets clicked in the child svelete component

Parent.astro

<script>    function updateBtn(){        //Display Button    }</script><div><div><Scomponent onclick="updateBtn()"/></div><button style="display=none">Click</button></div>

Scomponent.svelete (Svelete Component)

<div><button>Svelete button</button></div>