Hello Manon, 

Please try adding this custom HTML to the page where you have your Amelia shortcode: 

<style>
.amelia-app-booking input[type="text"], .am-modal.am-in-body input[type="text"], .amelia-app-booking input[type="email"], .am-modal.am-in-body input[type="email"], .amelia-app-booking input[type="tel"], .am-modal.am-in-body input[type="tel"], .amelia-app-booking input[type="url"], .am-modal.am-in-body input[type="url"], .amelia-app-booking textarea, .am-modal.am-in-body textarea, .amelia-app-booking select, .am-modal.am-in-body select, .amelia-app-booking .form-control, .am-modal.am-in-body .form-control, .amelia-app-booking .am-stripe-card, .am-modal.am-in-body .am-stripe-card,
.amelia-app-booking h1, .am-modal.am-in-body h1, .amelia-app-booking h2, .am-modal.am-in-body h2, .amelia-app-booking h3, .am-modal.am-in-body h3, .amelia-app-booking h4, .am-modal.am-in-body h4, .amelia-app-booking p, .am-modal.am-in-body p, .amelia-app-booking span, .am-modal.am-in-body span, .amelia-app-booking div, .am-modal.am-in-body div, .amelia-app-booking section, .am-modal.am-in-body section, .amelia-app-booking ul, .am-modal.am-in-body ul, .amelia-app-booking li, .am-modal.am-in-body li, .amelia-app-booking a, .am-modal.am-in-body a {font-family:fantasy !important;}
</style>

We have set font fantasy as an example but you will change it to your font. 

Let me know if this helped!

You are welcome, Manon. 

Great, glad to hear that!

If you have any other questions or concerns feel free to open a new ticket and we will gladly help,