I’m loving the fact that you get all the options you need and then are able to customize it using CSS. No connections to a third party, no nonsense. I’ve customized the colors to match my site:

/* review background color */
.grw-review-inner.grw-backgnd.grw-round.grw-shadow {
  background-color: #313131de!important;
}

/* "review us" button */
.wp-gr .wp-google-wr a {
  color: white!important;
  text-shadow: 0 0 0 !important;
  background: #c39d63!important;
}
.wp-gr .wp-google-wr:hover a {
  color: white!important;
  text-shadow: 0 0 0 !important;
  background: #c39d63de!important;
}

/* reviewer */
.wp-gr.wpac a.wp-google-name {
  color: #c39d63!important;
}

/* rating number */
.wp-gr .wp-google-rating {
  color: #c39d63!important;
  font-size:16px!important;
  vertical-align: sub!important;
}

/* rating stars */
.wp-star path {
  fill: rgb(195, 157, 99);
}

/* "based on" */
.wp-gr .wp-google-powered {
  color: #a3a3a3!important;
}

/* read more */
.wp-gr .wp-more-toggle {
  color: #c39d63 !important;
}

/* rounded square logo instead of circle */
.wp-gr.wpac .grw-header .wp-google-left img {
  height:80px!important;
  width:80px!important;
  border-radius: 30%!important;
  background-color:rgba(31,31,31,0.8)!important; 
  box-shadow:0 0 0!important
}

/* scroll dot color */
.wp-gr .grw-dot.active {
  background: #c39d63!important;
}

/* scroll arrow color */
.wp-gr .grw-btns svg path {
  fill: #c39d63;
}

/* hide Google logo in review */
.wp-gr .grw-review-inner>svg {
  visibility: hidden;
}

/* scrollbar width in review */
.wp-gr .grw-review .wp-google-feedback {
    scrollbar-width: thin;
    height: 100px!important;
    overflow-y: auto!important;
}