Answers for "change page width inside a iframe html"

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>

set iframe height and width by js

#IFRAME_ID {
  width: 100%!important;
  height: 100%!important;
}
<iframe src="http://www.youraddress.com" id="IFRAME_ID"></iframe>

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If still not working you can try solution from on the solutions from the link
https://stackoverflow.com/questions/819416/adjust-width-and-height-of-iframe-to-fit-with-content-in-it