@behnam_tr gave you the answer in message #2.
Here are the steps you can take to make it work:
1. copy the stylesheets line in the Main module (see highlighted line):
Sub AppStart (Form1 As Form, Args() As String)
MainForm = Form1
MainForm.Stylesheets.Add(File.GetUri(File.DirAssets, "styles.css"))
MainForm.Show
Dim PagesManager As B4XPagesManager
PagesManager.Initialize(MainForm)
End Sub
2. create a styles.css file (with an editor like Notepad++ for instance) and copy the styles information from message #2 into it.
.combo-box .list-cell {
-fx-text-fill: red;
}
.combo-box {
-fx-prompt-text-fill: red;
}
.combo-box .arrow-button .arrow {
-fx-background-color: red;
}
.combo-box .label {
-fx-text-fill: white;
}
In the highlighted lines i have changed the colors: red in stead of white and white in stead of yellow.
Save the styles.css file and add it in the Files Manager of the IDE.
3. Add the ComboBox in the designer and set the color (=background color) to lightblue for instance. Generate the member.
4. In the B4XMainPage module (B4XPage_Created subroutine) you can write some code to fill the ComboBox:
Dim lst As List = Array As String("item 1","item 2","item 3")
ComboBox1.Items.AddAll(lst)
ComboBox1.SelectedIndex = 0
5. run the application.
Note: when you check the ComboBox property Editable in the designer then the textfield text will not take the red color.