Edit in JSFiddle

var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');

ctx.fillStyle = 'lime';
canvas.style.background = "black";

var code = [
    'html','head','title','base','link','meta','style','script',
    'noscript','body','section','nav','article','aside','h1','h2',
    'h3','h4','h5','h6','hgroup','header','footer','address','main',
    'p','hr','pre','blockquote','ol','ul','li','dl','dt','dd',
    'figure','figcaption','div','a','em','strong','small','s','cite',
    'q','dfn','abbr','data','time','code','var','samp','kbd','sub',
    'sup','i','b','u','mark','ruby','rt','rp','bdi','bdo','span','br',
    'wbr','ins','del','img','iframe','embed','object','param','video',
    'audio','source','track','canvas','map','area','svg','math',
    'table','caption','colgroup','col','tbody','thead','tfoot','tr',
    'td','th','form','fieldset','legend','label','input','button',
    'select','datalist','optgroup','option','textarea','keygen',
    'output','progress','meter','details','summary','command','menu'
];
    
// make 100 things to fall with a random code element and random starting location
var tags = [];
var count = 100;

for (var i = 0; i < count; i++) {
    var a = {};
    // randomly pick one tag
    a.code = code[Math.round(Math.random() * code.length)];
    a.x = Math.random() * 500; // random X
    a.y = Math.random() * 500 - 500; // random Y that is above the screen
    a.speed = Math.random() * 10;
    tags.push(a);
}

setInterval(function() {
    ctx.clearRect(0, 0, 500, 500);
    
    for (var i = 0; i < count; i++) {
        var a = tags[i];
        ctx.fillText(a.code, a.x, a.y);
        a.y += a.speed; // fall downwards by the speed amount
        if (a.y > 600) a.y = -50; // if off the screen at bottom put back to top
    }
}, 90);

<canvas id="canvas" width="500" height="500"></canvas>

* { margin: 0; padding: 0; }
body { color: green; }