stylesheet_url where to define ?

tried that and it worked kind of but do we have to also input anything in the themes.php ?

seems my color.css is overiding my images.css

in themes.php they have defined

$current_stylesheet_dir = $themes[$current_theme][‘Stylesheet Dir’];
$current_stylesheet = $themes[$current_theme][‘Stylesheet’];

I also notice in admin when i click themes, the default css appears to be color.css vs style.css