Question: The code below creates a dialog window with a `QSplitter`.
The left and right side of splitter is assigned a dark-colored `QWidget`.
Each `QWidget` layout's spacing was set to 0 (zero) (so there should be no margin).
To each of these 0-spacing layouts there was a light colored QLabel added.

I want `QLabel` to fill an entire `QWidget` with no spacing or margin. So `QLabel` would expand and to extend from edge to edge. Ideally we would not see the dark color of the QWidget. How could we modify the code so the `QLabel` extends from edge to edge inside of QWidget?

[![enter image description here](https://i.stack.imgur.com/H574v.png)](https://i.stack.imgur.com/H574v.png)

```
from PyQt5.QtCore import *
from PyQt5.QtGui import *
from PyQt5.QtWidgets import *

app = QApplication([])
window = QDialog()
window.setLayout(QVBoxLayout())
window.resize(400, 250)

splitter = QSplitter(Qt.Horizontal)
window.layout().addWidget(splitter)

for side in ['left', 'right']:
    widget = QWidget()
    widget.setStyleSheet("background-color:gray;")
    widget_layout = QVBoxLayout()
    widget_layout.setSpacing(0)
    widget.setLayout(widget_layout)
    label = QLabel('%s side QLabel' % side.capitalize())
    label.setAlignment(Qt.AlignCenter)
    label.setStyleSheet("background-color:lightgray;")
    widget.layout().addWidget(label)
    splitter.addWidget(widget)

window.show()
sys.exit(app.exec_())

```

Answer: 
You must set the layout margins to 0:

```
widget_layout.setContentsMargins(0, 0, 0, 0)

```

Code:

```
app = QApplication(sys.argv)
window = QDialog()
window.setLayout(QVBoxLayout())
window.resize(400, 250)

splitter = QSplitter(Qt.Horizontal)
window.layout().addWidget(splitter)

for side in ['left', 'right']:
    widget = QWidget()
    widget.setStyleSheet("background-color:gray;")
    widget_layout = QVBoxLayout()
    widget_layout.setContentsMargins(0, 0, 0, 0) # this line
    widget_layout.setSpacing(0)
    widget.setLayout(widget_layout)
    label = QLabel('%s side QLabel' % side.capitalize())
    label.setAlignment(Qt.AlignCenter)
    label.setStyleSheet("background-color:lightgray;")
    label.setContentsMargins(0, 0, 0, 0)
    widget.layout().addWidget(label)
    splitter.addWidget(widget)

window.show()
sys.exit(app.exec_())

```

Screenshot:

[![enter image description here](https://i.stack.imgur.com/WZl1W.png)](https://i.stack.imgur.com/WZl1W.png)

*Note:* `setSpacing()` is unnecessary in this case since this indicates the space between widgets inside a layout, but in this case only the `QLabel` is only in the layout.
You can also use:
`splitter->setHandleWidth(1);`