Media queries not working inside an iframe

Question

I have in a webpage which is responsive. It makes use of media queries.

But the same page loaded in an iframe is not working.

For example, consider to my web

Answer 1

Try it this way, instead of device just target the width

Change

@media only screen and (max-device-width : 640px) {

to

@media only screen and (max-width : 640px) {

Also, it is more advised to target both min and max view-port width if you want to avoid considering order of media query declarations in your style-sheet

@media screen and (min-width: 320px) and (max-width: 640px) {
    .header-text {
       background-color: blue;
    }
}