Hello @tilou,
If you want customize the appearance of all dropdown fields, the selector would be:
#fbuilder .cff-dropdown-field select{}
But if you want customize the appearance of only one dropdown field, assign to it a custom class name, for example: my-field (the class names are assigned to the fields through the “Add CSS Layout Keywords” attribute in their properties), and the selector in this case would be:
#fbuilder .my-field select{}
The styles definitions are entered into the “Customize Form Design” attribute in the “Form Settings” tab (https://cff.dwbooster.com/images/documentation/form-settings-tab.png)
For example, assuming you want change the background color of the field to yellow, the style definition would be:
#fbuilder .my-field select{background-color: yellow;}
If you need a custom coding service to customize the appearance of your form, do not hesitate in contact me through my private website:
https://cff.dwbooster.com/customization
Best regards.