Use more readable font-sizes for overviews and guides (#214)

Author: jelbourn

src/styles/_markdown.scss

@@ -2,18 +2,26 @@
 
 .docs-markdown-h1 {
   display: inline-block;
-  font-size: 20px;
+  font-size: 34px;
   font-weight: 400;
   padding: 5px;
 }
 
+.docs-markdown-h2 {
+  font-size: 24px;
+}
+
+.docs-markdown-h3 {
+  font-size: 20px;
+}
+
 .docs-markdown-h2,
 .docs-markdown-h4 {
   margin-top: 40px;
 }
 
 .docs-markdown-h5 {
-  font-size: 16px;
+  font-size: 18px;
 }
 
 .docs-markdown-p {
@@ -26,7 +34,7 @@
 }
 
 .docs-markdown-td code {
-  font-size: 12px;
+  font-size: 14px;
 }
 
 .docs-markdown-pre {
@@ -49,7 +57,7 @@ code, pre {
 }
 
 pre {
-  font-size: 12px;
+  font-size: 14px;
 }
 
 .docs-header-link {