script.js

function color(){
	for(i = 0; i < 70; i++){
		switch (document.getElementsByTagName("marquee")[i].style.color){
			case "aqua":
				document.getElementsByTagName("marquee")[i].style.color = "blue";
				break;
			case "blue":
				document.getElementsByTagName("marquee")[i].style.color = "purple";
				break;
			case "purple":
				document.getElementsByTagName("marquee")[i].style.color = "pink";
				break;
			case "pink":
				document.getElementsByTagName("marquee")[i].style.color = "white";
				break;
			case "white":
				document.getElementsByTagName("marquee")[i].style.color = "gray";
				break;
			case "gray":
				document.getElementsByTagName("marquee")[i].style.color = "red";
				break;
			case "red":
				document.getElementsByTagName("marquee")[i].style.color = "orange";
				break;
			case "orange":
				document.getElementsByTagName("marquee")[i].style.color = "yellow";
				break;
			case "yellow":
				document.getElementsByTagName("marquee")[i].style.color = "green";
				break;
			default:
				document.getElementsByTagName("marquee")[i].style.color = "aqua";
		}
	}

}

var fullscreenBtn = document.getElementById('fullscreen-btn');

fullscreenBtn.addEventListener('click', function() {
    if (document.fullscreenElement || document.webkitFullscreenElement ||
        document.mozFullScreenElement || document.msFullscreenElement) {
        exitFullscreen();
    } else {
        requestFullscreen();
    }
});

function requestFullscreen() {
    var element = document.documentElement;
    if (element.requestFullscreen) {
        element.requestFullscreen();
    } else if (element.webkitRequestFullscreen) {
        element.webkitRequestFullscreen();
    } else if (element.mozRequestFullScreen) {
        element.mozRequestFullScreen();
    } else if (element.msRequestFullscreen) {
        element.msRequestFullscreen();
    }
}

function exitFullscreen() {
    if (document.exitFullscreen) {
        document.exitFullscreen();
    } else if (document.webkitExitFullscreen) {
        document.webkitExitFullscreen();
    } else if (document.mozCancelFullScreen) {
        document.mozCancelFullScreen();
    } else if (document.msExitFullscreen) {
        document.msExitFullscreen();
    }
}