Custom CSS styling

Hi, I’m trying to change the background color of dropdown options and on hover colors but it’s not just changing. Can you guide me here?
Here’s what I’m seeing right now: http://kreativecodes.xyz/back.jpg

I need the background white to be changed to #222222 and the font color to be white.

I’m using the following code but it’s not taking any effect.

select{
        background: #222;
        color:#ffffff;
    }
    option:not(:checked) { 
        background-color: #222; 
    }