[DiapDealer]

A crash course for those who roll their own Sigil and want to get a head start on dark-theming their PyQt5 plugins:

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

def dark_palette(sigil_colors):
    p = QPalette()
    dark_color = QColor(sigil_colors("Window"))
    disabled_color = QColor(127,127,127)
    dark_link_color = QColor(108, 180, 238)
    text_color = QColor(sigil_colors("Text"))
    p.setColor(p.Window, dark_color)
    p.setColor(p.WindowText, text_color)
    p.setColor(p.Base, QColor(sigil_colors("Base")))
    p.setColor(p.AlternateBase, dark_color)
    p.setColor(p.ToolTipBase, dark_color)
    p.setColor(p.ToolTipText, text_color)
    p.setColor(p.Text, text_color)
    p.setColor(p.Disabled, p.Text, disabled_color)
    p.setColor(p.Button, dark_color)
    p.setColor(p.ButtonText, text_color)
    p.setColor(p.Disabled, p.ButtonText, disabled_color)
    p.setColor(p.BrightText, Qt.red)
    p.setColor(p.Link, dark_link_color)

    p.setColor(p.Highlight, QColor(sigil_colors("Highlight")))
    p.setColor(p.HighlightedText, QColor(sigil_colors("HighlightedText")))
    p.setColor(p.Disabled, p.HighlightedText, disabled_color)

    return p

class MyQWidget(QWidget):
    def __init__(self, bk, prefs):
        blah
        blah
        blah

def run(bk):
    prefs = bk.getPrefs()
    supports_theming = (bk.launcher_version() >= 20200117)
    app = QApplication(sys.argv)
    if supports_theming:
        if bk.colorMode() == "dark":
            # The Windows Sigil darkmode is created with the Fusion style as
            # the basis for Sigil's dark palette. Macs may prefer starting elsewhere.
            # Though "Fusion" should suffice for all three platforms without a lot of fuss.
            app.setStyle(QStyleFactory.create("Fusion"))
            app.setPalette(dark_palette(bk.color))
    ex = MyQWidget(bk, prefs)
    ex.show()
    app.exec_()

Clearly you'd have to create your own MyQWidget class in this case, but I leave that up to you. There's many ways tackle creating PyQt5 plugin interfaces. That's nothing to do with theming. I should have a working version of my DOCXImport plugin that will support dark-mode ready for uploading soon. So people will be able to copy/paste from that as well.