width of screen to iframe code example
Example: how to show iframe in full width
<div>
<div style="position:relative;padding-top:56.25%;">
<iframe src="https://www.youtube.com/embed/nckseQJ1Nlg" frameborder="0" allowfullscreen
style="position:absolute;top:0;left:0;width:100%;height:100%;"></iframe>
</div>
</div>