So many browsers so many different screen resolutions. Here’s a way to modify html code based on the screen resolution of the browser. In this example I have changed an image but there is no reason why you cant change text, font size or even use it to redirect users who have mobile sized screens.
if ((screen.width>=1280) && (screen.height>=720))
document.write("<img src=\"images/pic.png\" />");
document.write("<img src=\"images/picsmall.png\" />");
Remember to check your landing pages on all screen resolutions. Users with crappy displays still convert and if you’re landing page looks rubish on them you are losing ROI.