Source code iframe html responsive

I want Source code for iframe css responsive for all mobiles and tab and laptop
I searched a lot, but I could not find the code that fits all devices
Whoever knows the source code or has a way to send it

Set the width and height attributes on the iframe to the largest dimensions you want. e.g. 1000px. Then in CSS set

width: 100%;
max-width: 1000px;

Adjust the figures to suit your needs.