Hi,
You can add these lines to Custom CSS or the style.css of Child Theme.
.upsells .owl-nav div,.cross-sells .owl-nav div {
position: absolute;
top: 50%;
-moz-transform: translate(0, -50%);
-webkit-transform: translate(0, -50%);
-ms-transform: translate(0, -50%);
-o-transform: translate(0, -50%);
transform: translate(0, -50%);
-webkit-border-radius: 0;
-moz-border-radius: 0;
border-radius: 0;
height: 44px;
width: 44px;
padding: 0;
background-color: rgba(128, 128, 128, 0.5);
text-align: center;
-webkit-transition: all 0.35s ease;
-o-transition: all 0.35s ease;
transition: all 0.35s ease;
}
.upsells .owl-nav div i,.cross-sells .owl-nav div i {
font-size: 24px;
color: #fff;
line-height: 44px;
}
.upsells .owl-nav div:hover,.cross-sells .owl-nav div:hover {
background-color: #4c7e6f;
}
.upsells .owl-nav .owl-prev,.cross-sells .owl-nav .owl-prev {
left: -10px;
}
.upsells .owl-nav .owl-next,.cross-sells .owl-nav .owl-next {
right: -10px;
}
Thanks.