width in percent

[exdeniz]

 new Custombox.modal({
      content: {
        effect: 'fadein',
        target: 'https://www.youtube.com/watch?v=HLMDVHX7Ctg&t=165s',
        width: '80%',
      },
    }).open()

and

<iframe src="https://www.youtube.com/embed/HLMDVHX7Ctg" frameborder="0" allowfullscreen="" width="80px" height="45px"></iframe>