hcmenu.css

.highcharts-menu > hr {
    display: block !important;
    border: 1px gray solid !important;
    margin-block-start: 0.5em !important;
    margin-block-end: 0.5em !important;
    margin-inline-start: auto !important;
    margin-inline-end: auto !important;
    -moz-float-edge: margin-box !important;
    box-sizing: content-box !important;
}