<canvas width="200" height="200" id="plano"></canvas> 
#plano{
  width: 50%;
  margin: 0 auto;
  display: block;
  border: 1px solid #d9d9d9;
}
var canvas = document.getElementById("plano");
var X,Y;

inicializarCanvas();

function inicializarCanvas(){ 
  var ctx = canvas.getContext("2d");
  X=canvas.width/2;
  Y=canvas.height/2;
  dibujar(ctx);
}

function dibujar(ctx){
  ctx.fillStyle = "#108EFF";
  ctx.arc(X,Y,X,0,2*Math.PI);
  ctx.fill();
}  

External CSS

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External JavaScript

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