pm-controls/source/app/controls/components/panels/resize-panel/resize-panel.css

ProModel Controls

.resize-panel-container {
    display: flex;
    height: 100%;
    width: 100%;
}

.resize-panel-item-container {
    overflow: auto;
    flex-basis: 0px;
    flex-shrink: 1;
    height: 100%;
}


.custom-thumb-vertical {
    width: 10px;
    background-color: red;
    height:100%;
    cursor: ew-resize; 
    z-index: 1;
} 

.custom-thumb-vertical:after {
  content: "\f142"; 
  font-family: FontAwesome;
  font-style: normal;
  font-weight: normal;
  text-decoration: inherit;
  position: relative;
  font-size: 15px;
  color: blue;
  top: 45%;
  left: 30%; 
  z-index: 2;
}