Customize material-ui popover [duplicate]
Try adding this to your css file
.popover_class{ margin-top: 10px; border: 1px solid black;}.popover_class::before{ content: ''; position: absolute; top: -20px; right: 5px; border-bottom: 10px solid black; border-right: 10px solid transparent; border-left: 10px solid transparent; border-top: 10px solid transparent; z-index: 10;}
add tyhis style in style css. You have only to adjust some margin and colors.
.popover_class:after {content:"";position: absolute;right: 4px;top: -5px;width: 0;`height: 0;border-style: solid;border-width: 0 8px 8px 8px;border-color: transparent transparent green transparent;z-index:9998;}