Drop margins on expression builder

src/ui/qgsexpressionbuilder.ui

@@ -20,6 +20,9 @@
    <string>Form</string>
   </property>
   <layout class="QGridLayout" name="gridLayout_2">
+   <property name="margin">
+    <number>0</number>
+   </property>
    <item row="0" column="0">
     <widget class="QSplitter" name="splitter_2">
      <property name="orientation">

src/ui/qgsexpressionbuilderdialogbase.ui

@@ -6,14 +6,17 @@
    <rect>
     <x>0</x>
     <y>0</y>
-    <width>625</width>
-    <height>554</height>
+    <width>507</width>
+    <height>539</height>
    </rect>
   </property>
   <property name="windowTitle">
    <string>Expression string builder</string>
   </property>
   <layout class="QGridLayout" name="gridLayout">
+   <property name="margin">
+    <number>3</number>
+   </property>
    <item row="0" column="0">
     <widget class="QgsExpressionBuilderWidget" name="builder" native="true">
      <property name="autoFillBackground">

src/ui/qgsexpressionselectiondialogbase.ui

@@ -14,6 +14,9 @@
    <string>Select By Expression</string>
   </property>
   <layout class="QGridLayout" name="gridLayout">
+   <property name="margin">
+    <number>3</number>
+   </property>
    <item row="1" column="0">
     <spacer name="horizontalSpacer">
      <property name="orientation">