Hi,

Please refer : https://prnt.sc/tgtcna

Get into Admin Panel > Appearance > Customize > Additional CSS > Paste the below css code inside the text area > Save All.

.breadcrumb { background-color: #000;}
.breadcrumb:before { background: none !important;}
.breadcrumb:after { background: none !important;}
.breadcrumb-section:before { background: none !important;}
.breadcrumb-section:after { background: none !important;}