.field-related_papers .selector {
    width: 1200px;
    float: left;
}

.field-related_papers .selector select {
    width: 580px;
    height: 17.2em;
}

.field-related_papers .selector-available, 
.field-related_papers .selector-chosen {
    float: left;
    width: 580px;
    text-align: center;
    margin-bottom: 5px;
}