ol-dark-rounded.css

:root,
:host {
  --ol-background-color: black;
  --ol-accent-background-color: #F5F5F5;
  --ol-subtle-background-color: rgba(128,128,128,.25);
  --ol-partial-background-color: rgba(0,0,0,.75);
  --ol-foreground-color: white;
  --ol-subtle-foreground-color: rgba(255,255,255,.95);
  --ol-brand-color: #00AAFF;
}

.ol-control,
.ol-control button,
.ol-zoom .ol-zoom-in, 
.ol-zoom .ol-zoom-out,
.ol-overviewmap-map,
.ol-overviewmap-map .ol-viewport {
  border-radius: 100%;
}

.ol-scale-line,
.ol-scale-line-inner,
.ol-zoomslider,
.ol-attribution,
.ol-mouse-position {
  border-radius: 1.375em;
}

.ol-zoom.ol-control {
  background-color: unset;
}

.ol-zoomslider {
  height: calc(200px + 0.6875em);
}

.ol-zoomslider button {
  height: 1.375em;
}

.ol-overviewmap .ol-overviewmap-map {
  border: 2px solid var(--ol-partial-background-color);
}

.ol-mouse-position {
  background-color: var(--ol-subtle-background-color);
  padding: 0.2em 0.6em;
}