Full screen QWebEngine without margins?

I am trying to get QWebEngine to fill the entire window. Per this answer I am trying to use setContentsMargins(0,0,0,0); with the result below: the QWebEngine loads the page at full window size but then immediately scales down to this:

When I use setContentsMargins(1,1,1,1); with the QWebEngine in the layout, it loads correctly, with a 1 px margin. I did a test of just loading the image directly, with no margin and it loaded fine and filled the screen.

Is this my bug/issue or QWebEngine's?

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QtWebEngineWidgets>

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    QVBoxLayout *mainLayout = new QVBoxLayout;
    mainLayout->setContentsMargins(0,0,0,0);
    ui->centralWidget->setLayout(mainLayout);

//    // load and show image
//    inputImg = new QImage(":/images/testScreen.jpg");
//    imgDisplayLabel = new QLabel("");
//    imgDisplayLabel->setPixmap(QPixmap::fromImage(*inputImg));
//    imgDisplayLabel->adjustSize();
//     mainLayout->addWidget(imgDisplayLabel);

    view = new QWebEngineView(this);
     mainLayout->addWidget(view);

    QUrl url;
    url = QUrl("qrc:/testScreen.html");
    view->load(url);
}