compact-unified-extensions.css

#unified-extensions-view {
  --uei-icon-size: 16px;

  > .panel-header {
    display: none !important;

    + toolbarseparator {
      border-top: none !important;
      margin-bottom: var(--arrowpanel-menuitem-margin-inline) !important;
    }
  }

  .unified-extensions-item {
    margin-block: 0 !important;

    .unified-extensions-item-message-deck {
      display: none;
    }

    > .unified-extensions-item-menu-button {
      list-style-image: url("chrome://global/skin/icons/more.svg") !important;
      padding: 0 0 0 var(--arrowpanel-menuitem-margin-inline) !important;

      > .toolbarbutton-icon {
        border: none !important;
      }
    }
  }
}

preview.markdown