#cevrele{
width:500px;
margin:0 auto;
position:relative;
}
#siyah-cerceve{
position:relative;
width:500px;
border:3px solid black;
height:250px;
display:block;
}
#mavi-cerceve{
position:absolute;
bottom:-20px;
height:30px;
width:400px;
left:50px;
border:3px solid blue;
background:white;
}
#kirmizi-cizgi{
width:500px;
margin:0 auto;
height:2px;
background:red;
}