#legend_panel_content {
  min-height: 400px;
}

.layer_legend_header {
    display: table;
    text-align: left;
}

.layer_legend_container {
    border: 0;
}

.legend_image {
    text-align: left;
}

.legend_image>img {
    min-width: 20px;
    min-height: 20px;
}

.layer_legend_source_label {
    position: absolute;
    width: 10em;
    right: 15px;
    text-align: right;
}

#legend_panel_content {
  height: 400px;
  overflow-y: auto;
}

.layer_legend_header {
    display: table;
    text-align: left;
}

.layer_legend_container {
    border: 0;
}

.legend_image {
    text-align: left;
}

.legend_image>img {
    min-width: 20px;
    min-height: 20px;
}

.layer_legend_source_label {
    position: absolute;
    width: 10em;
    right: 15px;
    text-align: right;
}

Use scrollbar in legend dialog
Use scrollbar in legend dialog
