sam elh on "Change Display on Mobile Detect"

Hello Coders !
sorry i am not really into PHP, but i'd like to ask for help..
what should i add in the comment line of the following code, to make an item appear? for example if the user uses mobile, a button id="btn" will change display style from none to block .. i can do this but only using Js and onclick.. any help ? here's the code :

<?php
if ( wp_is_mobile() ) {
	/* Display and echo mobile specific stuff here */
}
?>

in an other way, i don't want to show the button for desktop users. Thank Ya'll !