body {background-color:gray; }

div.container {top: 0; left: 0; width: 100%; height: 100%;
    position: fixed; display: table}
p {display: table-cell; vertical-align: middle}

  /* Horizontal centering of image: set left & right margins to 'auto' */
img.displayed{display: block;
margin: 1em auto;
width:900px;
border:5px solid blue;}

table.centerme{
margin: 1em auto;
border:5px solid blue;}

  /* Also center the lines in the paragraph */
  p {text-align: center}