title: Checked symbol in checkbox is not visible unless the element is hover
body: <p>In a Qt application, I have a button which later with some code I attach a menu to it. Each element of the menu is a checkable <code>QAction</code>. The interesting thing is that once the element is check, the check sign isn't visible unless you hover it with the mouse. Here is a screenshot:</p>
  
  <p><img src="https://i.stack.imgur.com/L4onc.png" alt="enter the image"></p>
  
  <p>I have some custom QCSS set, however, I have never added any style for <code>QAction</code> or anything, here it is:</p>
  
  <pre><code>QMainWindow, QDialog { background: #E8E8E8; color: #2e2e2e; }
  
  QMenuBar, QStatusBar {
      background: #545454;
      color: #fff;
  }
  
  QLabel#lblBanner {
      background: qlineargradient(x1: 0, y1: 0.01, x2: 0, y2: 1,
                                  stop: 0 #545454, stop: 1 #141414);
      margin: 0;
  }
  
  QMenu {
      background: #E8E8E8;
  }
  QMenuBar::item {
      background: transparent;
  }
  
  QMenuBar::item:selected {
      background: #444442;
      border: 0;
  }
  
  QMenuBar::item:pressed {
      background: #444442;
  }
  
  QMenu::item:selected {
      background: #cfcfcf;
  }
  
  QGroupBox {
      background: #fff;
      /* border: 1px solid white; */
      border-radius: 5px;
      margin: 3px 3px 3px 3px;
      padding: 18px 5px 10px 5px;
      font-weight: bold;
  }
  
  QGroupBox::title {
      subcontrol-origin: margin;
      subcontrol-position: top left;
      color: black;
      font-style: bold;
      /* padding: 4px 5px; */
      margin-left: 6px;
      margin-top: 7px;
      background: transparent;
      color: #2e2e2e;
  }
  
  QPushButton, QDialogButtonBox {
      background: qlineargradient(x1: 0, y1: 0, x2: 0, y2: 1,
                                  stop: 0 #f5f5f5, stop: 1 #cfcfcf); 
      border-radius: 3px;
      padding: 5px 10px;
      margin: 1px;
      min-width: 30px ;
  }
  
  QPushButton:hover, QDialogButtonBox:hover {
      background: qlineargradient(x1: 0, y1: 0, x2: 0, y2: 1,
                                  stop: 0 #cfcfcf, stop: 1 #b5b5b5);
  }
  
  QPushButton:pressed, QDialogButtonBox:pressed {
      background: qlineargradient(x1: 0, y1: 0, x2: 0, y2: 1,
                                  stop: 0 #b5b5b5, stop: 1 #cfcfcf);
  }
  
  QPushButton:default, QDialogButtonBox:default {
      border: 1px solid;
      border-color: orange; /* make the default button prominent */
  }
  
  QPushButton[enabled=false]
  {
      background: #ededed;
      color: #cfcfcf;
  }
  
  QLineEdit, QTextEdit {
      background: qlineargradient(x1: 0, y1: 0, x2: 0, y2: 0.3,
                                  stop: 0 #f2f2f2, stop: 1 white);
      border: 2px solid #E8E8E8;
      selection-background-color: orange;
      border-radius: 5px;
      padding: 3px;
  }
  
  QHeaderView::section {
      background-color: qlineargradient(x1: 0, y1: 0.01, x2: 0, y2: 1,
                                        stop: 0 #545454, stop: 1 #141414);
      color: white;
      padding-left: 10px;
      border: 1px solid #6c6c6c;
  }
  
  QTreeWidget {
      border: 2px solid #E8E8E8;
      border-radius: 5px;
      selection-background-color: orange;
      show-decoration-selected: 1;
  }
  
  /* QTreeWidget::item:selected { */
  /*     background: ; */
  /* } */
  
  QTreeWidget::item:selected:!active {
      background: #e59500;
  }
  
  QTreeWidget::item:selected:active {
      background: #f29d00;
  }
  
  QTreeWidget::item:hover {
      background: orange;
  }
  
  QTreeWidget::branch {
      background: white;
  }
  
  /* barra de desplazamiento */
  /* Vertical */
  QScrollBar:vertical {
      background: #fff;
      width: 10px;
  }
  
  QScrollBar::handle:vertical {
      background: #E8E8E8;
  }
  
  /* Horizontal */
  QScrollBar:horizontal {
      background: #fff;
      height: 10px;
  }
  
  QScrollBar::handle:horizontal {
      background: #E8E8E8;
  }
  /* Fin de la barra de desplazamiento */
  
  QProgressBar {
      border: 2px solid orange;
      border-radius: 5px;
      background: #fff;
      text-align: center;
  }
  
  QProgressBar::chunk {
      background: orange;
      margin: 2px;
      border-radius: 5px;
  }
  </code></pre>
  
  <p>What can be the problem and in which way could I fix this?</p>