The following worked for me:
*Keep in mind first you have to activate the announcement bar.
For linear gradient:
.sqs-announcement-bar {
background: linear-gradient(to left, #dd8d96 0%, #0d3ac7 100%) !important;
}
For circular gradient:
.sqs-announcement-bar {
background: radial-gradient(circle, #dd8d96 0%, #0d3ac7 100%) !important;
}
*just change the color codes