Add a note above the neuroglancer viewer

Author: kabilar

src/css/custom.css

@@ -150,6 +150,13 @@
   overflow: hidden;
 }
 
+.viewer-card-note {
+  font-size: 0.9rem;
+  color: var(--ifm-color-emphasis-900);
+  margin-top: -0.5rem;
+  margin-bottom: 0.5rem;
+}
+
 .viewer-card-mobile-message {
   display: none;
 }

src/pages/mri-xray.mdx

@@ -28,5 +28,6 @@ hide_table_of_contents: true
 
 <div className="viewer-card">
   <h3>🔍 Explore the data</h3>
+  <p className="viewer-card-note">Each layer can be toggled on and off by selecting its name. Note that some layers may take a few moments to load.</p>
   <iframe src="https://neuroglancer-demo.appspot.com/#!https://dandiarchive.s3.amazonaws.com/blobs/f6b/759/f6b75920-36c0-403e-a8a1-200d66a9e00d" title="Neuroglancer" allow="fullscreen"></iframe>
 </div>