[DPC-5220] Set ToS background color to white (#2919)

## 🎫 Ticket

https://jira.cms.gov/browse/DPC-5220

## 🛠 Changes

Sets the background color for the Terms of Service component to white.

## ℹ️ Context

This provides contrast with the rest of the page.

## 🧪 Validation

local:
<img width="888" height="785" alt="image"
src="https://github.com/user-attachments/assets/1e809afd-c2dd-4db9-b7af-36db3ec560e9"
/>

Approved by product review.

---------

Co-authored-by: jdettmannnava <145699825+jdettmannnava@users.noreply.github.com>

Author: ashley-weaver

dpc-portal/app/components/page/organization/tos_form_component.html.erb

@@ -2,7 +2,7 @@
 <div>
   <h2>Sign Terms of Service</h2>
   <p>Once you sign our Terms of Service, <%= @organization.name %> will be allowed to access Medicare claims data.</p>
-  <div style="width: 100%; height: 420px; overflow-y: auto; border: 2px solid silver; padding: 1rem;" class="margin-bottom-5">
+  <div style="width: 100%; height: 420px; overflow-y: auto; border: 2px solid silver; padding: 1rem;" class="margin-bottom-5 bg-white">
     <%= render Core::TosContent::TosContentComponent.new %>
   </div>
 

dpc-portal/spec/components/page/organization/tos_form_component_spec.rb

@@ -18,7 +18,7 @@
         <div>
           <h2>Sign Terms of Service</h2>
           <p>Once you sign our Terms of Service, Health Hut will be allowed to access Medicare claims data.</p>
-          <div style="width: 100%; height: 420px; overflow-y: auto; border: 2px solid silver; padding: 1rem;" class="margin-bottom-5">
+          <div style="width: 100%; height: 420px; overflow-y: auto; border: 2px solid silver; padding: 1rem;" class="margin-bottom-5 bg-white">
             <div class="usa-prose measure-5">
               <section class="ds-l-container ds-u-padding-top--7 ds-u-padding-bottom--7">