Hi @axsu!
More than fixing the background color (which isn’t really possible, it’ll get lighter and lighter as the number of posts increase over time), what you want is to make the text readable. To do so you’ll need to change the styling of the link in a way that it provides enough contrast so people can actually read it.
At the moment the only way to make styling changes to the Midnight theme (or any other widget theme) is via PHP filter hooks (I plan to add another solution that should make it easier on a future update, for now this is the only way.) Use the wpp_additional_theme_styles filter hook to add your custom CSS rules and change the styling of links, like so for example:
/**
* Make popular posts links red in 'Midnight' theme.
*
* @param string $additional_styles
* @param string $theme_name
* @return string
*/
function wpp_additional_css_rules($additional_styles, $theme_name){
if ( 'midnight' == $theme_name ) {
$additional_styles .= '.wpp-list li a { color: red; }';
}
return $additional_styles;
}
add_filter('wpp_additional_theme_styles', 'wpp_additional_css_rules', 10, 2);
If you have any questions don’t hesitate to ask.