.trening_oczu {
  display:block;
  width:100%;
  height:80vh;
  border:solid 1px #aaa;
  position:relative;
}

.box {position:absolute; width:800px; height:800px; border: solid 1px #aaa; top:50%; left:50%; margin-top:-400px; margin-left:-400px;}
.line_horizontal { position:absolute; display:block; top:400px; width:800px; height:1px; background-color:#aaa;}
.line_vertical { position:absolute; display:block; left:400px; width:1px; height:100%; background-color:#aaa;}
.ball {position: absolute; left:370px; top:370px; width:60px; height:60px; border-radius: 50%; background-color:red; animation-name: myAnimation;animation-duration: 90s;}

@keyframes myAnimation {
  from {left: 370px; top:370px;}
  to {left: 0px; top:370px;}
}