qt dark style: fix padding of PayToEdit

based on Electron-Cash/Electron-Cash@7e69f0e6eaad2679850ad297dcd7fa31a7262a4f
see ColinDuquesnoy/QDarkStyleSheet#159

electrum/gui/qt/__init__.py

@@ -56,6 +56,7 @@ from .installwizard import InstallWizard, WalletAlreadyOpenInMemory
 from .util import get_default_language, read_QIcon, ColorScheme
 from .main_window import ElectrumWindow
 from .network_dialog import NetworkDialog
+from .stylesheet_patcher import patch_qt_stylesheet
 
 
 class OpenFileEventFilter(QObject):
@@ -132,6 +133,8 @@ class ElectrumGui(Logger):
             except BaseException as e:
                 use_dark_theme = False
                 self.logger.warning(f'Error setting dark theme: {repr(e)}')
+        # Apply any necessary stylesheet patches
+        patch_qt_stylesheet(use_dark_theme=use_dark_theme)
         # Even if we ourselves don't set the dark theme,
         # the OS/window manager/etc might set *a dark theme*.
         # Hence, try to choose colors accordingly:

electrum/gui/qt/stylesheet_patcher.py

@@ -0,0 +1,18 @@
+"""This is used to patch the QApplication style sheet.
+It reads the current stylesheet, appends our modifications and sets the new stylesheet.
+"""
+
+from PyQt5 import QtWidgets
+
+
+def patch_qt_stylesheet(use_dark_theme: bool) -> None:
+    if not use_dark_theme:
+        return
+
+    app = QtWidgets.QApplication.instance()
+
+    style_sheet = app.styleSheet()
+    style_sheet = style_sheet + '''
+    QAbstractScrollArea { padding: 0px; }
+    '''
+    app.setStyleSheet(style_sheet)