Floating Button with Icon

Site URL: https://panacherentals.squarespace.com

Hi, my client would like the floating "Contact Us" button to have a little mail icon. I figured out the coding for the button but would love help adding an svg icon to it. They sent me the website below as an example.

https://www.parisforrent.com/

First, edit your HTML code to this

<div id="book-me">
  <a href="/contact"><svg class="olark-envelope-icon" width="32" height="32" viewBox="0 0 32 32" aria-hidden="true" focusable="false" role="img" fill="none"><rect x="3" y="7" width="26" height="18" rx="2" stroke="currentcolor" stroke-width="2" stroke-linejoin="round"></rect><path d="M7 11L16 17L25 11" stroke="currentcolor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"></path></svg> Contact Us! </a>
</div>

Next, edit your CSS code to this

#book-me {
    position: fixed;
    top: 50%;
    left: 85%;
    transform: none;
    transform-origin: 100% 0;
    z-index: 99999;
}
#book-me a {
    background: #7f99c8;
    color: #fff;
    font-size: 14px;
    font-weight: bold;
    text-transform: uppercase;
    font-family: montserrat;
    padding: 17px 33px;
    border-radius: 25px;
    display: flex;
    align-items: center;
}
#book-me svg {
    margin-right: 5px;
}

Thank you so so much!! @tuanphan