請(qǐng)問(wèn)我這段代碼哪里有錯(cuò)誤，為什么畫(huà)不出圓來(lái)

html代碼

? ? ?<div class="step">

? ? ? ? ? <canvas id="steps" width="440" height="90"></canvas>

? ? ?</div>

js代碼

? ? window.onload = function(){

? ? ? ? var canvas = document.getElementById("steps");

????????var cxt = canvas.getContext('2d');

? ? ? ? canvas.width =440;

? ? ? ? canvas.height = 90;

????????cxt.fillStyle="red";

????????cxt.arc(45, 45, 25, 0, 2*Math.PI, false);

????????cxt.fill();

}