Fix #1960438 [[Enhancement] Windows have more top padding than others](https://bugs.launchpad.net/calibre/+bug/1960438)

src/calibre/gui2/convert/bulk.py

@@ -105,6 +105,7 @@ class BulkConfig(Config):
         for w in widgets:
             w.set_help_signal.connect(self.help.setPlainText)
             w.setVisible(False)
+            w.layout().setContentsMargins(0, 0, 0, 0)
 
         self._groups_model = GroupModel(widgets)
         self.groups.setModel(self._groups_model)

src/calibre/gui2/convert/heuristics.ui

@@ -213,6 +213,19 @@
      </layout>
     </widget>
    </item>
+   <item>
+    <spacer name="verticalSpacer">
+     <property name="orientation">
+      <enum>Qt::Vertical</enum>
+     </property>
+     <property name="sizeHint" stdset="0">
+      <size>
+       <width>20</width>
+       <height>40</height>
+      </size>
+     </property>
+    </spacer>
+   </item>
   </layout>
  </widget>
  <resources/>

src/calibre/gui2/convert/single.py

@@ -240,6 +240,7 @@ class Config(QDialog):
         for w in widgets:
             w.set_help_signal.connect(self.help.setPlainText)
             w.setVisible(False)
+            w.layout().setContentsMargins(0, 0, 0, 0)
 
         self._groups_model = GroupModel(widgets)
         self.groups.setModel(self._groups_model)

src/calibre/gui2/preferences/conversion.py

@@ -101,6 +101,7 @@ class Base(ConfigWidgetBase):
 
         for w in widgets:
             w.changed_signal.connect(self.changed_signal)
+            w.layout().setContentsMargins(6, 6, 6, 6)
             sa = QScrollArea(self)
             sa.setWidget(w)
             sa.setWidgetResizable(True)