Comment 2 for bug 888901

Using the following CSS prevents the issue from appearing:

.progressbar,
.progressbar row,
.trough,
.trough row {
 -unico-inner-stroke-gradient: none;
 -unico-inner-stroke-width: 0;

 -unico-outer-stroke-gradient: none;
 -unico-outer-stroke-width: 0;
}