How to select QWidget by class

Question

Imagine, that I want to set a css style to some QWidgets in MainWindow, for example:

QPushButton {
    background: rgb(79, 79, 79);
}

But it applies css style to all QPushButtons, I would like to set background only to some QPushButtons identified by some class. How to do it?

Edit:

        <widget class="QPushButton" name="pushButton_2">
         <property name="sizePolicy">
          <sizepolicy hsizetype="Minimum" vsizetype="Fixed">
           <horstretch>0</horstretch>
           <verstretch>0</verstretch>
          </sizepolicy>
         </property>
         <property name="minimumSize">
          <size>
           <width>0</width>
           <height>60</height>
          </size>
         </property>
         <property name="text">
          <string>Label</string>
         </property>
        </widget>

Answer 1

you need to use class selector

https://www.w3schools.com/cssref/sel_class.asp

QPushButton.someClass{
     background: rgb(79, 79, 79);
}

html will be e.g.

<QPushButton class='someClass'>
    Label
</QPushButton>