body {
  background: blue;
}

#strona {
  width: 900px;
  height: 620px;
  margin: auto;
  background-color: white;
}

#naglowek {
  background-color: lightblue;
  width: 900px;
  height: 100px;
  }

#menu {
  background-color: lightgray;
  width: 200px;
  height:500px;
  float: left;
}

#tresc {
  background-color: cyan;
  width: 700px;
  height:500px;
  float: left;
}


#stopka { 
  background-color: lightblue;
  width: 900px;
  height: 20px;
  float: left;
}