twocol_stacked.css in Panels 5

.panel-2col-stacked { 
  /* border: 1px solid red; */ 
  overflow: hidden; 
}

.panel-2col-stacked div > div {
  margin: .5px;
}

.panel-2col-stacked .panel-col-top,
.panel-2col-stacked .panel-col-bottom {
  width: 99.9%;
  clear: both;
}
.panel-2col-stacked .panel-col-first {
  float: left;
  width: 47%;
}
.panel-2col-stacked .panel-col-last {
  float: right;
  width: 47%;
}
.panel-clearer {
  clear: both;
}