Update 30 August 2019 Hello theme is missing img { height: auto }, added below.

CSS I added to the Hello theme, the only dark theme in the micro.blog theme gallery. It even has a light/dark switcher! See modifications at m.rdela.com (if you are coming from elsewhere).

img {
 display: block;
 max-width: 100%;
 height: auto; /* hello theme is missing height: auto */ 
}
.logo__cursor,
.logo__mark,
.footer .copyright span:first-child {
  display: none;
}
body.dark-theme {
  background: #000;
}
.dark-theme .header,
.header {
  background: transparent;
}
.content {
flex-direction: column;
flex: 1 auto;
align-items: center;
margin: 40px 0;
padding: 0 20px;
}
p.h-entry,
.post {
width: 100%;
max-width: 760px;
text-align: left;
padding: 20px 0 40px;
margin: 0 auto 20px;
}
p.h-entry:not(:last-of-type),
.post:not(:last-of-type) {
border-bottom: 1px solid #dcdcdc;
border-bottom: 1px solid var(--light-border-color);
}
.dark-theme p.h-entry:not(:last-of-type),
.dark-theme .post:not(:last-of-type) {
border-color: #4a4b50;
border-color: var(--dark-border-color);
}
.post-content {
margin-top: 20px;
}
.post-content p:last-of-type {
margin-bottom: 0;
}
.post-meta {
font-size: 1rem;
margin: 0;
}
.post-title {
font-size: 1.875rem;
margin: 0;
}

.logo__cursor hides the blinky “cursor,” down with all blinky things

.logo__mark gets rid of the > shaped SVG thing in front of the site name

.footer .copyright span:first-child hides the incorrect “Powered by Hugo” link.

body.dark-theme and .dark-theme .header darken the background from #292a2d and #252627 to true black (#000) for enhanced contrast and battery saving on mobile devices with OLED screens. To make the light theme header transparent, which looks better and more pleasantly minimal to me, we add plain .header in addition to the more specific .dark-theme .header, which we need to override a preexisting more specific declaration.

Do you think I should PR any of these changes? (See live at m.rdela.com.) Or are they worthy of a new theme? I could alter or remove those elements altogether instead of hiding them. I have a few more ideas for changes to the color and text scale/sizing as well. Suggestions welcome!