Change the transcript link color so it is readable

Note: this needs updating to make it obvious that it's a link. It
currently isn't.
diff --git a/pages/_app.js b/pages/_app.js
index 6784bdf..f09cb57 100644
--- a/pages/_app.js
+++ b/pages/_app.js
@@ -15,6 +15,7 @@
         text: '#424242',
         background: '#ffffff',
         primary: '#6576CC',
+        highlight: '#78ECF2',
         cardText: '#ffffff',
         cardBackground: 'rgba(255, 255, 255, 0.65)',
         cardBorder: '#C4C4C4',
@@ -33,6 +34,7 @@
                 text: '#ffffff',
                 background: '#000000',
                 primary: '#6576CC',
+                highlight: '#78ECF2',
                 cardText: '#424242',
                 cardBackground: 'rgba(0, 0, 0, 0.65)',
                 cardBorder: '#424242',