div.left
   {
   height:1px;
   clear:left;
   float:left;
   background-color:#9999ff;
   }
div.right
   {
   height:1px;
   clear:right;
   float:right;
   background-color:#9999ff;
   }
.
.
.
var r = 250;
var border = 165;
var rSquared = r * r;
var x;
var margin;

for (var y = r; y > 0; --y)
   {
   x = r - Math.sqrt (rSquared - y * y) + border;
   margin = (y > r-5) ? 0 : 6;
   document.write ("<div class='left' style='width:" + x + "px; margin-right:" + margin + "px;'></div>");
   document.write ("<div class='right' style='width:" + x + "px; margin-left:" + margin + "px;'></div>");
   }
for (y = 0; y <= r; ++y)
   {
   x = r - Math.sqrt (rSquared - y * y) + border;
   margin = (y > r-5) ? 0 : 12;
   document.write ("<div class='left' style='width:" + x + "px; margin-right:" + margin + "px;'></div>");
   document.write ("<div class='right' style='width:" + x + "px; margin-left:" + margin + "px;'></div>");
   }