.flex-container {
  display: flex;
  flex-direction: row;
  background-color: DodgerBlue; /* xroma giro apo kathe koutaki */
}

.flex-container > div {
  background-color: #f1f1f1; /* xroma mesa sto kouti */
  
  /* rythmiseis koutiou */
  margin: 10px;
  padding: 20px;
  font-size: 30px;
}

/* Responsive layout - ayto kanei na emfanizontai to ena katw apo to allo se mikres othones */
@media (max-width: 800px) {
  .flex-container {
    flex-direction: column;
  }
}