Change 'Contact Us' button to clickable telephone icon / number

Site URL: https://badger-wisteria-g5yn.squarespace.com/

Hi there,
I have just started working on this site for a client: https://badger-wisteria-g5yn.squarespace.com/ and I want to change the 'contact us' button on the top right to a clickable - telephone icon & telephone number.  
It would be great if anyone could advise what css coding I can use to achieve this?
Please note the site is very much in the beginning stages of development! 
Any thoughts would be much appreciated. 
Many thanks.

Hi @harriethoult, the answer somewhat depends on the template you are using. If you go into Settings > Site Availability you can set the site to Password Protected and share the password with us. Then someone may be able to help.

Hi @christyprice, thank you very much for your response. I have just set the password as 'mint' - all in lower-case. Any help would be great. 
Thanks!

Hi @harriethoult, 

Unfortunately, the workaround I use in Squarespace 7.0 with FontAwesome to get icons in the header no longer works in 7.1. 😞

Maybe someone else has another idea for you!

To change button link to telephone, add this to Home > Settings > Advanced > Code Injection Header

<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.4.1/jquery.min.js"></script>
<script>
$(document).ready(function(){
    $(".theme-btn--primary-inverse").attr("href", "tel:0123456789");
});
</script>

To change to telephone icon, add this to Home > Design > Custom CSS

.theme-btn--primary-inverse {
    background-image: url(https://static.thenounproject.com/png/3158715-200.png) !important;
    background-size: contain !important;
    background-repeat: no-repeat !important;
    background-position: center center !important;
    color: transparent !important;
    padding-left: 5px;
    padding-right: 5px;
}

@tuanphan thanks very much for your suggestions, I will give this a go. 
 - and thank you @christyprice for your responses. Hopefully we'll all be up to speed with 7.1 soon! 🙂