def add_separator(self):
"""
Add an horizontal line to layout.
"""
separator = QFrame()
separator.setFrameShape(QFrame.HLine)
separator.setFrameShadow(QFrame.Sunken)
separator.setMinimumSize(self.width(), 2)
# Add to layout
self.main_layout.addWidget(separator, self.row, 0, 1, 5)
# Increment vertically position for next widget
self.row += 1
