a11y: #4985 .card-content make h3 style smaller than h2

Author: StephDriver

src/themes/material/assets/mat.css

@@ -406,6 +406,10 @@ h3 {
     font-size: 2.0rem;
 }
 
+.card-content > h3{
+    font-size: 20px;
+}
+
 h4 {
     font-size: 1.8rem;
     font-weight: 300;