Fix "New" dialog in dark themes.

Don't explicitly use white, use the "base" color.

Task-number: QTCREATORBUG-7435
Change-Id: I3fcfefd958857146b6f9b2ceef3376d2b582b807
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@nokia.com>
Reviewed-by: Robert Löhning <robert.loehning@nokia.com>

src/plugins/coreplugin/dialogs/newdialog.cpp

@@ -199,6 +199,9 @@ NewDialog::NewDialog(QWidget *parent) :
 
     setWindowFlags(windowFlags() & ~Qt::WindowContextHelpButtonHint);
     m_ui->setupUi(this);
+    QPalette p = m_ui->frame->palette();
+    p.setColor(QPalette::Window, p.color(QPalette::Base));
+    m_ui->frame->setPalette(p);
     m_okButton = m_ui->buttonBox->button(QDialogButtonBox::Ok);
     m_okButton->setDefault(true);
     m_okButton->setText(tr("&Choose..."));

src/plugins/coreplugin/dialogs/newdialog.ui

@@ -136,8 +136,8 @@
    </item>
    <item row="1" column="2">
     <widget class="QFrame" name="frame">
-     <property name="styleSheet">
-      <string notr="true">QFrame { background: white }</string>
+     <property name="autoFillBackground">
+      <bool>true</bool>
      </property>
      <property name="frameShape">
       <enum>QFrame::StyledPanel</enum>