Let me add one more thing for clarification.  I did use the WebCombo with our styles, to rule out our PrismComboBox from being the cause, and it behaved the same way using the skin below:

<ISWebCombo:WebCombo
    runat="server"
    AllowAutoDataCaching="true"
    LayoutSettings-AllowAddItem="false"
    LayoutSettings-AllowNavigationOnMouseWheel="true"
    LayoutSettings-AllowTextWrapping="false" 
    LayoutSettings-AlwaysShowAllRowsOnDropdown="true" 
    LayoutSettings-AlwaysShowHelpButton="false" 
    LayoutSettings-ColumnStyle-CssClass="ComboBoxFrame"
    LayoutSettings-ComboMode="SingleColumn"
    LayoutSettings-DropDownStyle-Active-CssClass="ComboBoxDropDown"
    LayoutSettings-DropDownStyle-Normal-CssClass="ComboBoxDropDown"
    LayoutSettings-DropDownStyle-Over-CssClass="ComboBoxDropDown" 
    LayoutSettings-EntryMode="Default"
    LayoutSettings-FrameStyle-Active-CssClass="ComboBoxFrame" 
    LayoutSettings-FrameStyle-Normal-CssClass="ComboBoxFrame" 
    LayoutSettings-FrameStyle-Over-CssClass="ComboBoxFrame" 
    LayoutSettings-ResultBoxStyle-CssClass="ComboBoxResultBox"
    LayoutSettings-ResultFrameStyle-CssClass="ComboBoxResultFrame" 
    LayoutSettings-RowStyle-Active-CssClass="ComboBoxActiveRow" 
    LayoutSettings-RowStyle-Normal-CssClass="ComboBoxNormalRow" 
    LayoutSettings-RowStyle-Over-CssClass="ComboBoxOverRow" 
    LayoutSettings-SelectedRowStyle-CssClass="ComboBoxSelectedRow" 
    LayoutSettings-StatusBoxStyle-CssClass="ComboBoxStatusBox"
    LayoutSettings-TextBoxStyle-Active-CssClass="ComboBoxTextBox" 
    LayoutSettings-TextBoxStyle-Normal-CssClass="ComboBoxTextBox" 
    LayoutSettings-TextBoxStyle-Over-CssClass="ComboBoxTextBox"  
    Height="18px">
</ISWebCombo:WebCombo>

Also, I'm including all the CSS styles referenced above which should help incase they're contributing to the problem.

.ComboBoxFrame
{
	border-color: #DDCCCC;
	border-width: 1px;
	border-style: solid;
	background-color: White;
	color: #666666;
}
.ComboBoxDropDown
{
	font-family: Webdings;
	border: none;
	background-color: white;
	color: #DDCCCC;
	cursor: pointer;
}
.ComboBoxResultBox
{
	border-style: none;
	background: #FFFFFF;
	font-size: 10pt;
	font-Family: Calibri;
	font-weight: lighter;
}
.ComboBoxResultFrame
{
	border-style: solid;
	border-color: #DDCCCC;
	border-width: 1px;
	background: #FFFFFF;
}
.ComboBoxActiveRow
{
}
.ComboBoxNormalRow
{
	background-color: #FFFFFF;
	font-size: 10pt;
	Font-Family: Calibri;
	font-weight: lighter;
	color: #666666;
}
.ComboBoxOverRow
{
	background-color: #CCBBAA;
	font-size: 10pt;
	Font-Family: Calibri;
	font-weight: lighter;
	color: #666666;
}
.ComboBoxStatusBox
{
	background-color: #EEEEEE;
	font-size: 10pt;
	font-Family: Calibri;
	font-weight: lighter;
}
.ComboBoxTextBox
{
	Font-Size: 10pt;
	font-Family: Calibri;
	border-width: 0px;
	border-style: none;
	border-collapse: collapse;
	background-color: #FFFFFF;
	color: Black;
}

Hi Arthur,

I think the style would not have different in Unbound or bound mode. Please run my attached sample. I tried to follow your css styles and the only problem is your ColumnStyle. I noticed that the background colour is white. That's why i don't see any colors when hover in each rows. In fact, when i Comment out the style, I can see that SelectedRowStyle works fine. Please let me know if you have the same result or not.

Regards,
Handy

Hello Handy,

I did get it working after you pointed me in the right direction, however, only when UseDefaultStyle is set to true.  When it's false, I can never get it to work.  In my skin file, the following line is now set to a different style:

Any ideas why I can't get it to work when not using the default style?  Thanks.

[EDIT] I forgot to mention that if you add the line to your sample, it will not work either, i.e.,

Hi Yousif,

Thank you also for pointing me more detail. :-)

I have discussed with our developer. This issue occurs because the limitation of ResultBoxWindowType Popup mode. This mode could not call Css class properly. 
I have two workarounds for this issue.

1. You will need set the style into each properties manually

such as:

BackColor="#DDCCBB" Font-Bold="True" Font-Names="Calibri" Font-Size="14pt" ForeColor="Red" 

2. You can change  ResultBoxWindowType Normal mode. I suggest you also to turn off ResultBoxShadow properties.

I hope my workarounds can help.

Regards,
Handy

Hello Handy,

Thank you for the workarounds.  I did not try #1 but am sure it'll work.  I did try #2 and it works.  Thank you.

Great, Glad to hear that. Thanks