关于 Qt 布局的问题

突然发现是 spacing，哎，结帖！！！

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如下图所示：

写了一个简单的布局，却不知为何多出来一块区域，试了很久也不知道这块区域是个啥，有知道的大佬还望指点！

窗体代码：

#include "mainwindow2.h"
#include "ui_mainwindow2.h"
#include <QVBoxLayout>
#include <QTextEdit>

MainWindow2::MainWindow2(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow2)
{
    ui->setupUi(this);

    setAttribute(Qt::WA_StyledBackground);

    ui->statusbar->showMessage("Hello World!");

    QVBoxLayout* mainLayout = new QVBoxLayout;
    mainLayout->setMargin(0);
    mainLayout->setContentsMargins(0, 0, 0, 0);

    QWidget* widget = new QWidget;
    widget->setObjectName("box");
    auto boxLayout = new QHBoxLayout(widget);
    boxLayout->setMargin(0);
    boxLayout->setContentsMargins(0, 0, 0, 0);

    auto textEdit = new QTextEdit;
    textEdit->setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Expanding);

    mainLayout->addWidget(widget);
    mainLayout->addWidget(textEdit);

    centralWidget()->setLayout(mainLayout);
}

MainWindow2::~MainWindow2()
{
    delete ui;
}

CSS 代码：

* {
  background-color: lightcoral;
}

#box {
  min-height: 49px;
  max-height: 49px;
  margin: 0px;
  border: 1px solid black;
  background-color: red;
}