use fixed position for error flash UI

video_metadata/static/style.css

@@ -8,7 +8,6 @@ nav h1 { flex: auto; margin: 0; }
 nav h1 a { text-decoration: none; padding: 0.25rem 0.5rem; }
 nav ul  { display: flex; list-style: none; margin: 0; padding: 0; }
 nav ul li a, nav ul li span, header .action { display: block; padding: 0.5rem; }
-.flash { margin: 1em 0; padding: 1em; background: #cae6f6; border: 1px solid #377ba8; }
 .content { padding: 0 1rem 1rem; }
 .content > header { border-bottom: 1px solid lightgray; display: flex; align-items: flex-end; }
 .content > header h1 { flex: auto; margin: 1rem 0 0.25rem 0; }
@@ -23,6 +22,12 @@ input.danger { color: #cc2f2e; }
 .file { background: orange; }
 .file_stored { background: lightgreen; }
 
+.flash {
+	position: fixed; bottom: 1em;
+	margin: 1em 0; padding: 1em; border: 1px solid #377ba8;
+	background: #cae6f6;
+}
+
 #query_result_container,
 .success_container {
 	position: fixed;