Fix datepicker style

jet/static/jet/css/jquery-ui/_jquery-ui.theme.scss

@@ -1,6 +1,7 @@
 @import "../globals";
 
 .ui-widget-content {
+  color: $text-color;
   border-color: $content-border-color;
 }
 
@@ -105,4 +106,23 @@
   opacity: 0.8;
   font-size: 13px;
   pointer-events: none;
-}
+}
+
+.ui-datepicker {
+  table {
+    margin: 0 0 .4em;
+    background: transparent;
+    border-radius: 0;
+    box-shadow: none;
+  }
+
+  th {
+    background: inherit;
+    color: inherit;
+    text-transform: inherit;
+  }
+
+  tbody tr {
+    border-bottom: inherit;
+  }
+}