style: fix expand-content font size and unify CTA copy

Set explicit font-size on .expand-content to prevent it inheriting
a smaller size from context. Standardize the two call-to-action labels
to "Submit a project" (lowercase, consistent phrasing).

Co-Authored-By: Claude <noreply@anthropic.com>

website/templates/index.html

@@ -12,7 +12,7 @@
           class="hero-topbar-link hero-topbar-link-strong"
           target="_blank"
           rel="noopener"
-          >Submit a Project</a
+          >Submit a project</a
         >
       </div>
     </div>
@@ -252,7 +252,7 @@
       class="hero-action hero-action-primary"
       target="_blank"
       rel="noopener"
-      >Read the contribution guide</a
+      >Submit a project</a
     >
     <a
       href="https://github.com/vinta/awesome-python"