fix(shoutouts): update background color for shoutout cards (#100)

Author: zwying0814

src/pages/shoutouts.astro

@@ -164,7 +164,7 @@ const allTestimonials = [...testimonials, ...extraTestimonials];
     padding: 20px;
     border-radius: 14px;
     border: 1px solid var(--border-subtle);
-    background: rgba(10, 15, 26, 0.7);
+    background: var(--surface-card-strong);
     backdrop-filter: blur(8px);
     text-decoration: none;
     color: var(--text-primary);