Column headings now black in mobile view, closes #729

datasette/static/app.css

@@ -79,6 +79,7 @@ table a:visited {
 
     .rows-and-columns td:before {
         display: block;
+        color: black;
         margin-left: -10%;
         font-size: 0.8em;
     }
@@ -349,4 +350,4 @@ p.zero-results {
 /* Value types */
 .type-float, .type-int {
     color: #666;
-}
+}