span.a {
  display: inline; /* the default for span */
  width: 100px;
  height: 100px;
  padding: 5px;
  border: 1px solid blue;  
  background-color: yellow; 
}

span.b {
  display: inline-block;
  width: 100px;
  height: 100px;
  padding: 5px;
  border: 1px solid blue;    
  background-color: #F1EFE2; 
}

span.c {
  display: block;
  width: 90%;
  height: 1em;
  padding: 5px;
  border: 1px solid blue;    
  background-color: #ffffff;
  overflow: hidden;
  margin-left: 20px;
}
span.c:hover {
  display: block;
  width: 90%;
  height: auto;
  padding: 5px;
  border: 1px solid blue;    
  background-color: #ffffff; 
  overflow: auto;
  margin-left: 20px;
}