[Security Solution][Onboarding] UI refresh - align footer and header icons colors (#208899)

## Summary

This PR addresses issue https://github.com/elastic/kibana/issues/205730

<img width="1117" alt="Screenshot 2025-01-30 at 11 08 11"
src="https://github.com/user-attachments/assets/1708e49b-af1d-4ebf-a112-5a5d7cb33c1c"
/>
<img width="983" alt="Screenshot 2025-01-30 at 11 09 30"
src="https://github.com/user-attachments/assets/7c1d14e4-2c07-4361-9f22-f59e729ddffa"
/>
<img width="1097" alt="Screenshot 2025-01-30 at 11 08 42"
src="https://github.com/user-attachments/assets/404d6e9c-efc5-43fd-a357-d4ca8a4cb40c"
/>
<img width="986" alt="Screenshot 2025-01-30 at 11 08 53"
src="https://github.com/user-attachments/assets/6a05b9b9-0ef9-4dda-a21e-610cd08026e0"
/>


### Checklist

Check the PR satisfies following conditions. 

Reviewers should verify this PR satisfies this list as well.

- [ ] [Unit or functional
tests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)
were updated or added to match the most common scenarios

---------

Co-authored-by: Elastic Machine <elasticmachine@users.noreply.github.com>

x-pack/solutions/security/plugins/security_solution/public/onboarding/components/onboarding_header/cards/common/link_card.styles.ts

@@ -28,6 +28,7 @@ export const useCardStyles = () => {
 
     .headerCardTitle {
       font-weight: ${euiTheme.font.weight.semiBold};
+      font-size: 1rem;
     }
 
     ${isDarkMode

x-pack/solutions/security/plugins/security_solution/public/onboarding/components/onboarding_header/cards/common/link_card.tsx

@@ -6,7 +6,7 @@
  */
 
 import React, { useCallback } from 'react';
-import { EuiCard, EuiImage, EuiLink, EuiSpacer, EuiText, EuiTitle } from '@elastic/eui';
+import { EuiCard, EuiImage, EuiLink, EuiSpacer, EuiText } from '@elastic/eui';
 import classNames from 'classnames';
 import { trackOnboardingLinkClick } from '../../../lib/telemetry';
 import { useCardStyles } from './link_card.styles';
@@ -50,11 +50,7 @@ export const LinkCard: React.FC<LinkCardProps> = React.memo(
             size={64}
           />
         }
-        title={
-          <EuiTitle size="xxs" className="headerCardTitle">
-            <h3>{title}</h3>
-          </EuiTitle>
-        }
+        title={<span className="headerCardTitle">{title}</span>}
         description={<EuiText size="xs">{description}</EuiText>}
       >
         <EuiSpacer size="s" />