title: Using Stylesheet in Python Pycharm
body: <p>I am trying this code and it works, but the code "setStyleSheet ..." doesn't. 
  It opens the window, but there is no border and no backgroundcolor change ... </p>
  
  <pre><code>import sys
  from PyQt5 import QtWidgets, QtCore, QtGui, QtCore, Qt
  
  
  class MainWindow():
      def __init__(self):
          self.app = QtWidgets.QApplication(sys.argv)
          self.window = QtWidgets.QMainWindow()
  
  
          self.window.setWindowTitle('Our first Button')
          self.window.setGeometry(400,100,400,500)
          self.window.setStyleSheet('border:3 px solid #4e4e4e; background-color:6e6e6e')
          self.window.show()
          sys.exit(self.app.exec_())
  
  
  main = MainWindow()
  </code></pre>