import flash.geom.*;

var fillType:String = "linear"

var colors:Array = [0xFF0000, 0x0000FF];

var alphas:Array = [100, 100];

var ratios:Array = [0x00, 0xFF];

var matrix:Matrix = new Matrix();

matrix.createGradientBox(20, 20, Math.PI / 2, 0, 0);

var spreadMethod:String = "pad";

this.beginGradientFill(fillType, colors, alphas, ratios, matrix, spreadMethod); 

this.moveTo(0, 0);

this.lineTo(0, 100);

this.lineTo(100, 100);

this.lineTo(100, 0);

this.lineTo(0, 0);

this.endFill();