Restyle Rich to fit in with Active Admin's style.

active_admin.css.scss

form .cke_chrome {
  display: inline-block;
  width: calc(80% - 2px);
  box-shadow: none;

  // border color needs additional specificity as it is set on .cke_n.cke_chrome
  border-color: #c9d0d6 !important;
}
.cke_chrome, .cke_inner {
  @include rounded;
}
.cke_top {
  @include rounded-top;
}
.cke_bottom {
  @include rounded-bottom;
}