I added this:
.tag #dgwork-page-header{background: transparent; box-shadow: none;}
.tag #dgwork-page-header h1{color:#000;}
to Appearance> Customize> Additional CSS along with
.search #dgwork-page-header{background: transparent; box-shadow: none;}
.search #dgwork-page-header h1{color:#000;}
which works.
Only the tags page won’t – still the default black background with particles.