downloads: make the VC++ redistributable warning more visible

dolweb/downloads/templates/downloads-index.html

@@ -36,8 +36,8 @@ <h1>{% trans "Development versions" %}</h1>
     use the latest and greatest improvements to the project. They are however
     less tested than stable versions of the emulator.</p>
 
-    <p>The development versions require the <a href="https://support.microsoft.com/en-us/help/2977003/the-latest-supported-visual-c-downloads">64-bit Visual C++ redistributable for Visual Studio 2019</a>
-    to be installed.</p>
+    <div class="alert alert-info">The development versions require the <a href="https://support.microsoft.com/en-us/help/2977003/the-latest-supported-visual-c-downloads">64-bit Visual C++ redistributable for Visual Studio 2019</a>
+    to be installed.</div>
 {% endblocktrans %}</div>
 
 {% include "downloads-devrel.html" with builds=master_builds primclass='btn-info' %}