Dark theme for Qt widgets?

There's no dark theme built into Qt. But you can quite easily create one yourself with the following code:

from PyQt5.QtCore import Qt
from PyQt5.QtWidgets import QApplication
from PyQt5.QtGui import QPalette, QColor


app = QApplication([])
# Force the style to be the same on all OSs:
app.setStyle("Fusion")

# Now use a palette to switch to dark colors:
palette = QPalette()
palette.setColor(QPalette.Window, QColor(53, 53, 53))
palette.setColor(QPalette.WindowText, Qt.white)
palette.setColor(QPalette.Base, QColor(25, 25, 25))
palette.setColor(QPalette.AlternateBase, QColor(53, 53, 53))
palette.setColor(QPalette.ToolTipBase, Qt.black)
palette.setColor(QPalette.ToolTipText, Qt.white)
palette.setColor(QPalette.Text, Qt.white)
palette.setColor(QPalette.Button, QColor(53, 53, 53))
palette.setColor(QPalette.ButtonText, Qt.white)
palette.setColor(QPalette.BrightText, Qt.red)
palette.setColor(QPalette.Link, QColor(42, 130, 218))
palette.setColor(QPalette.Highlight, QColor(42, 130, 218))
palette.setColor(QPalette.HighlightedText, Qt.black)
app.setPalette(palette)

The nice thing about this is that it introduces no external dependencies. If you're interested what the above changes look like, I created an example PyQt5 app with a dark theme. Here is a screenshot:

No, but you may use my fairly comprehensive stylesheets that should look excellent on most platforms (it's inspired by KDE's Breeze Theme, which is a dark theme that is quite elegant). This was (hard) forked from the excellent QDarkStylesheet, which I felt had theme issues in numerous areas, so I modified it extensively for my own needs and added a light theme.

Simple Use

A sample of the theme is here. To use it in PyQt5, simply add the following lines to a project:

import sys
from PyQt5.QtCore import QFile, QTextStream
from PyQt5.QtWidgets import QApplication
import breeze_resources

app = QApplication(sys.argv)
file = QFile(":/dark.qss")
file.open(QFile.ReadOnly | QFile.Text)
stream = QTextStream(file)
app.setStyleSheet(stream.readAll())

Dynamic Stylesheet Toggling

In response to a comment, the easiest way to adjust the stylesheet to use either the light or the dark stylesheet dynamically is to wrap it in a function. You may then use the function as a slot to a Qt signal (warning: I primarily develop using C++, so there may be small errors in my code for the signal/slot mechanism).

def toggle_stylesheet(path):
    '''
    Toggle the stylesheet to use the desired path in the Qt resource
    system (prefixed by `:/`) or generically (a path to a file on
    system).

    :path:      A full path to a resource or file on system
    '''

    # get the QApplication instance,  or crash if not set
    app = QApplication.instance()
    if app is None:
        raise RuntimeError("No Qt Application found.")

    file = QFile(path)
    file.open(QFile.ReadOnly | QFile.Text)
    stream = QTextStream(file)
    app.setStyleSheet(stream.readAll())

Now we can add generic application logic that can use this function in a signal/slot mechanism (using a lambda as a convenient wrapper, if needed, to provide the path to the stylesheet toggler):

# add logic for setting up application
app = QApplication(sys.argv)
# more logic for creating top-level widgets, application logic ...

parent = ...
light_btn = QPushButton("Toggle light.", parent)
light_btn.clicked.connect(lambda: toggle_stylesheet(":/light.qss"))

dark_btn = QPushButton("Toggle dark.", parent)
dark_btn.clicked.connect(lambda: toggle_stylesheet(":/dark.qss"))

# add to the layout, do other stuff
# ...

# end the Qt application
sys.exit(app.exec_())

This allows users to dynamically change the theme of an application developed with PyQt5 (or using analogous logic in C++, Qt5) to either a light or dark theme.

Disclaimer: Obviously I am the maintainer.