.square, .circle {
width: 100px;
height: 100px;
}
.circle {
border-radius: 50%;
}

#blockRed {
background-color: red;
}
#blockYellow {
background-color: yellow;
}

.square, .circle {
width: 100px;
height: 100px;
display: block;
}

#container {
background-color: blue; margin: 0 auto;
width: 400px;
}

#blockRed {
background-color: red;
position: relative;
}
#blockYellow {
background-color: yellow;
position: relative;
}

<div class='square' id='blockRed' style='top: 200px; left: 200px;'></div>