Decrease beta ribbon size and hide donate button for small screens

Since beta ribbon obstructed view of various pages, its size is decreased. Donate button overlaps with other links, thus it was hidden on small screens. Related #1477 (closed)

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Migrated from D1510 (view on Phabricator)

swh/web/assets/src/bundles/browse/browse.css

@@ -130,3 +130,11 @@ td.swh-branch-message {
 td.swh-branch-date {
     min-width: 250px;
 }
+
+@media screen and (max-width: 600px) {
+    .swh-corner-ribbon {
+        line-height: 30px;
+        top: 53px;
+        right: -65px;
+    }
+}