How to change background color to transparent

Question

There is js code of canvas effect and i want to make the background color transparent and place the video below the text

https://codepen.io/richardwestenra/pen/rZmERo

particleSystem.prototype.repaint = function() {
  // clear the screen
  this.ctx.fillStyle = '#1d1d1d';
  this.ctx.fillRect(0, 0, this.width, this.height);
};

When I try to change the background to transparent, a white background appears below the text.

particleSystem.prototype.repaint = function() {
  // clear the screen
  this.ctx.fillStyle = '#1d1d1d00';
  this.ctx.fillRect(0, 0, this.width, this.height);
};