I'm trying out RSC and want to trigger an overlay that says "Message Sent" when the form is sent.

I'm reading the docs but I'm a bit confused.

This is what I have so far and it works the email gets sent but not sure how to trigger an UI update.
I don't want to trigger a redirect since this is a static website with one page

import { FormInput } from './Input'

export default function Form() {
  async function sendMessage(data) {
    'use server'

    const formDataObj = {}
    for (let [name, value] of data.entries()) {
      if (name === 'name' || name === 'email' || name === 'message') {
        formDataObj[name] = value
      }
    }

    return await sendSESMail(formDataObj)
  }

  return (
    <form action={sendMessage} className='flex flex-col gap-4 z-2'>
      <FormInput
        label='Your Name'
        type='text'
        name='name'
        placeholder='John Doe'
        required={true}
      />
      <FormInput
        label='Your Email'
        type='email'
        name='email'
        placeholder='john.doe@email.com'
        required={true}
      />
      <label htmlFor='message' className='flex flex-col gap-2'>
        <span className='text-brand-white'>Your Message</span>
        <textarea
          name='message'
          className='p-2 bg-brand-white'
          placeholder='Your message here...'
          rows={5}
          required={true}
        />
      </label>

      <button className='bg-brand-gold p-2 mt-4' type='submit'>
        Send Message
      </button>
    </form>
  )
}