Custom TabWidget button

[mero]

How can I create tab "+" like in firefox ?
plusff.png

I write something like this, but it looks different than in firefox

.cpp

TabManager::TabManager(QWidget *parent) : QTabWidget(parent)
{
    tab = tabBar();
...
    this->addTab(new QWidget(), QIcon("plus.png"), "");
...
}

TabManager::TabManager(QWidget *parent) : QTabWidget(parent)
{
    tab = tabBar();
...
    this->addTab(new QWidget(), QIcon("plus.png"), "");
...
}

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.h

class TabManager : public QTabWidget
{
    Q_OBJECT
public:
    TabManager(QWidget *);
 
private:
    QTabBar *tab;

class TabManager : public QTabWidget
{
    Q_OBJECT
public:
    TabManager(QWidget *);

private:
    QTabBar *tab;

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result is:

plus.png

so question is - do I need to change paint event for QTabWidget or QTabBar ?
or maybe there is another way to do that ?