问Qt设计器:无法更改字体大小

EN

HEADERS       = mainwindow.h 
FORMS         = mainwindow.ui 
RESOURCES     = stylesheet.qrc
SOURCES       = main.cpp \
                mainwindow.cpp \

<RCC>
<qresource prefix="/">
    <file>qss/cool.qss</file>
</qresource>
</RCC>

#include <QtWidgets>

#include "mainwindow.h"

int main(int argc, char *argv[])
{
    Q_INIT_RESOURCE(stylesheet);

    QApplication app(argc, argv);
    MainWindow window;
    window.show();
    return app.exec();
}

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QtWidgets>

#include "ui_mainwindow.h"

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow();

    Ui::MainWindow ui;

private:
    void loadStyleSheet(const QString &sheetName);
};

#endif

#include <QtWidgets>

#include "mainwindow.h"

MainWindow::MainWindow()
{
    ui.setupUi(this);
    loadStyleSheet("Cool");
}

void MainWindow::loadStyleSheet(const QString &sheetName)
{
    QFile file(":/qss/" + sheetName.toLower() + ".qss");
    file.open(QFile::ReadOnly);
    QString styleSheet = QString::fromLatin1(file.readAll());

    qApp->setStyleSheet(styleSheet);
}

QTabWidget::pane { /* The tab widget frame */
    border: 2px solid #C2C7CB;
}

QTabWidget::tab-bar {
    left: 5px; /* move to the right by 5px */
}

/* Style the tab using the tab sub-control. Note that
    it reads QTabBar _not_ QTabWidget */
QTabBar::tab {
    background: qlineargradient(x1: 0, y1: 0, x2: 0, y2: 1,
                                stop: 0 #E1E1E1, stop: 0.4 #DDDDDD,
                                stop: 0.5 #D8D8D8, stop: 1.0 #D3D3D3);
    border: 2px solid #C4C4C3;
    border-bottom-color: #C2C7CB; /* same as the pane color */
    border-top-left-radius: 4px;
    border-top-right-radius: 4px;
    /* You should change min-width according to the
        lenght of your tab text */
    min-width: 14ex;
    padding: 4px;
    font: bold 14px;
}

QTabBar::tab:selected, QTabBar::tab:hover {
    background: qlineargradient(x1: 0, y1: 0, x2: 0, y2: 1,
                                stop: 0 #fafafa, stop: 0.4 #f4f4f4,
                                stop: 0.5 #e7e7e7, stop: 1.0 #fafafa);
}

QTabBar::tab:selected {
    border-color: #9B9B9B;
    border-bottom-color: #C2C7CB; /* same as pane color */
}

QTabBar::tab:!selected {
    margin-top: 2px; /* make non-selected tabs look smaller */
}

font: bold 14px;