Klaviyo Waitlist Button

Hi!

We are using the Showcase theme.

The code for the waitlist button: 

 <script src="https://a.klaviyo.com/media/js/onsite/onsite.js"></script>
<script>
  var klaviyo = klaviyo || [];
  klaviyo.init({
    account: "Public ID Key - Redatched for this Thread",
    platform: "shopify"
  });
  klaviyo.enable("backinstock", { 
    trigger: {
      product_page_text: "Notify Me When Available",
      product_page_class: "button button--full-width",
      product_page_text_align: "center",
      product_page_margin: "0px",
      replace_anchor: false
    },
    modal: {
      headline: "{product_name}",
      body_content: "Register to receive a notification when this item comes back in stock.",
      email_field_label: "Email",
      button_label: "Notify me when available",
      subscription_success_label: "You're in! We'll let you know when it's back.",
      footer_content: '',
      additional_styles: "@import url('https://fonts.googleapis.com/css?family=Helvetica+Neue');",
      drop_background_color: "#000",
      background_color: "#fff",
      text_color: "#222",
      button_text_color: "#fff",
      button_background_color: "#439fdb",
      close_button_color: "#ccc",
      error_background_color: "#fcd6d7",
      error_text_color: "#C72E2F",
      success_background_color: "#d3efcd",
      success_text_color: "#1B9500",
      button_styles: {
        font_size: "16px", 
        font_family: "Helvetica Neue",
        background_color: "#439fdb",
        color: "#fff", 
        padding: "12px 24px",
        border_radius: "4px",
        margin_top: "10px",
        margin_bottom: "10px"
      }

I would love love for it to have the same appearance as our Sold Out Button - half width and white and act the same way as the sold out button. Rather than Sold Out appearing - join the waitlist appears in its place!

Thank you so so much!
    }
  });
</script>