I did instructions in "responsive webpages(RW)"( https://www.w3schools.com/html/html_responsive.asp ) and checked my webpage in https://www.w3schools.com/howto/howto_css_devices.asp . However, my website did not shown in iframe when I changed the code in "try it" page, it showed white blank page with no error.
When I changed my web-browser's size(i.e adjust it near the tablet size), does this do the trick of check RW, or do I need other things to do? Thanks.