Change background of DateField via code behind

[RandProgrammer]

Hello, I have a problem changing the background of a DateField (the DateFieldTo in the aspx code) in the codebehind...

This is my aspx code:

        <ext:FieldContainer ID="FieldContainer2" runat="server" FieldLabel='Validity Period' Split="true" Layout="ColumnLayout">
		<Items>
            <ext:DateField runat="server" ID="DateFieldFrom" 
                ColumnWidth=".5" MinWidth="100" Vtype="daterange"
                PaddingSpec="0 3 0 0" Name="ValidFrom" AllowBlank="false">
                <CustomConfig>
                    <ext:ConfigItem Name="endDateField" Value="DateFieldTo" Mode="Value" />
                </CustomConfig>
			</ext:DateField>
			<ext:Label ID="Label2" runat="server" Text='-' />

                         <%--This is the DateField that I want to change the background--%>
			<ext:DateField runat="server" ID="DateFieldTo" 
                ColumnWidth=".5" MinWidth="100" Vtype="daterange"
                PaddingSpec="0 0 0 3" Name="ValidTo" AllowBlank="true">
                <CustomConfig>
                    <ext:ConfigItem Name="startDateField" Value="DateFieldFrom" Mode="Value" />
                    </CustomConfig>
			</ext:DateField>
		</Items>
	</ext:FieldContainer>

this is what the code generates:


and this is what I want to achieve:


I've tried:

DateFieldTo.SetFieldStyle("background-color: rgb(255, 243, 199) !important;");

but it doesn't work in Chrome and Firefox, am I doing something wrong?