feat: improve style in preview pane (#256)

Author: smeijer

src/styles/app.pcss

@@ -256,6 +256,19 @@ button:disabled {
   @apply text-base p-1 mb-2;
 }
 
+.preview hr {
+  @apply my-4;
+}
+
+.preview h1,
+.preview h2,
+.preview h3,
+.preview h4,
+.preview h5,
+.preview h6 {
+  @apply font-bold mb-2;
+}
+
 .preview .highlight {
   @apply shadow-outline rounded;
 }