How to optimize redundant selectors with gulp-cssnano (or else) - css

Question

[gulp-minify-css says quite cleary, that is has been deprecated in favor of gulp-cssnano.]
I am quite happy with thi css minification of cssnano, except for two things..
identical selectors with no interference otherwise do not get merged, i.e. body, html or h1, h2, h3 in the sample below
identical media query-‘brackets’ are not joined into one big query bracket, i.e. #media only screen and (max-width:500px)
even certain overrulings even on the very same selectors and precedence are not pruned (i.e. color:orange over green for h1,h2,h3)
Any advice, how to achieve this optimisation with cssnano.co ? (or another minification gulp task to chain into)
body,html{
margin:0;
padding:0;
}
h1,h2,h3{
color:green;
background-color:#caa;
}
#media only screen and (max-width:500px){
p{
background-color:orange;
}
}
#media only screen and (max-width:500px){
div,p{
background-color:purple;}
}
body,html{
margin:0;
padding:0;
background-color:#aac;
}
h1,h2,h3{
font-weight:700;
color:orange;
text-decoration:underline;
}
html{
background:orange;
}
h1,h2,h3{
font-weight:700;
}
p{
text-decoration:none;
color:#eee;
}
(This example is coming from three rather trivial files, merged together. core:false to keep whitespace. Turning it on removes whitespace, but does not fix the mentioned issues. )