I want to use the Willow template, i try the whole day to get my background in the Main Content Container TRANSPARENT... no way

my custom.css:
body {
background-image: url("https://www.speicher-tuebingen.de/images/bg/3069_2534x1690.jpg") !important;
}
>> correct loading the image as Background...
but
.maincontent {
background-color: rgb(0,255,0);opacity:0.2;
}
neither
.com-content-article {
background-color: rgba(60,60,60,0.5);
}
... show me a transparent Background.
Please Help!
Regards, Markus.