How to specify the way a code snippet is marked up?

Question

Goal

For documentation purposes I would like to export a C++ code snippet from QtCreator as an HTML file and then use CSS to highlight its syntax, for example like that:

Since QtCreator does not have an export option, I am using QDoc to achieve that.

As per documentation, I use \quotefile in a qdoc-file in my project to turn the source code from main.cpp into an HTML:

/*!
    \page index
    \quotefile main.cpp
 */

Running qdoc produces an index.html and when I open it, there is indeed the marked-up content of main.cpp.

Note: To demonstrate the issue I am using the code from the documentation:

#include <QApplication>
#include <QPushButton>

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    QPushButton hello("Hello world!");
    hello.resize(100, 30);

    hello.show();
    return app.exec();
}

Problem

When I inspect the produced html code in the browser, for the hello( part for example, I get:

 hello(

When I inspect the html code of the documentation however, which I believe is generated with the help of QDoc as well, for the same part I see:

<span class="pln"> hello</span>

I do not know why in my case the additional markup is missing.

Question

How to setup QDoc so, that I can specify the rules of how each part of the code snippet should be marked up?