Check out https://kevin.deldycke.com/2012/04/beautify-contextual-related-posts-wordpress-plugin/
You can use that code as one option.
Another option:
img.crp_thumb {
width:50px !important;
height:50px !important;
display:block;
float:left;
clear:left;
margin-right:10px !important;
padding:3px !important;
border:1px #CCCCCC solid;
}
#crp_related ul li, .crp_related ul li {
clear:both;
list-style:none;
margin-bottom:15px;
display:block;
height:70px;
background: none;
padding:0 !important;
}
#crp_related ul, .crp_related ul {
margin:0 !important;
padding:0 !important;
}
#crp_related .crp_title, .crp_related .crp_title {
font-weight:bold;
font-size:14px;
display:block;
padding-bottom:5px;
text-decoration:none;
}
img.crp_thumb:after {
content: ' ';
width: 100%;
height: 100%;
position: absolute;
top: -1px;
left: -1px;
border: solid 1px #222;
-wekbit-box-shadow: inset 0 0 1px rgba(255,255,255,.4), inset 0 1px 0 rgba(255,255,255,.4), 0 1px 2px rgba(0,0,0,.3);
-moz-box-shadow: inset 0 0 1px rgba(255,255,255,.4), inset 0 1px 0 rgba(255,255,255,.4), 0 1px 2px rgba(0,0,0,.3);
box-shadow: inset 0 0 1px rgba(255,255,255,.4), inset 0 1px 0 rgba(255,255,255,.4), 0 1px 2px rgba(0,0,0,.3);
-webkit-border-radius: 7px;
-moz-border-radius: 7px;
border-radius: 7px;
}
img.crp_thumb {
vertical-align: bottom;
-webkit-box-shadow: 0 1px 2px rgba(0,0,0,.4);
-moz-box-shadow: 0 1px 2px rgba(0,0,0,.4);
box-shadow: 0 1px 2px rgba(0,0,0,.4);
-webkit-border-radius: 7px;
-moz-border-radius: 7px;
border-radius: 7px;
}
In both cases replace crp with tptn