did you explicitely declare the css classes?
<asp:TextBox ID="yourTxt" runat="server" Width="500px"></asp:TextBox>
<ajaxToolkit:AutoCompleteExtender ID="yourTxt_AutoCompleteExtender" runat="server"
FirstRowSelected="true" DelimiterCharacters="" Enabled="True" MinimumPrefixLength="3"
ServiceMethod="yourMethod" CompletionSetCount="5" CompletionInterval="300"
EnableCaching="true" CompletionListCssClass="autocomplete_completionListElement"
CompletionListItemCssClass="autocomplete_listItem" CompletionListHighlightedItemCssClass="autocomplete_highlightedListItem"
ServicePath="~/WS/yourWS.asmx" TargetControlID="yourTxt">
</ajaxToolkit:AutoCompleteExtender>
.autocomplete_completionListElement { visibility: hidden; margin: 0px !important; padding-left: 0px !important; background-color: #ffffff; color: #000000; border: buttonshadow; border-width: 1px; border-style: solid; cursor: default; overflow: auto; height: 100px; text-align: left; list-style-type: none; }
.autocomplete_highlightedListItem { background-color: #eee; color: black; padding: 1px; }
.autocomplete_listItem { background-color: #fff; color: #000; padding: 1px; }
that is working in my webapp
try F5 to reload the style...
best regards j