chrome extension help

so i've been working on a chrome extension that should change each word in a website to a different colour but for some reason it isn't working

i've been following this tutorial but it seems it might be outdated because i downloaded it and it doesn't work either (https://www.lateral.io/resources-blog/create-chrome-extension-modify-websites-html-css)

if anyone has advice or improvements pLease help thanks

var all_words = document.getElementsByTagName('P');
var individual_words = all_words.split(" ");
var colour_options = ["red", "purple", "blue"];
var spans = [];
for(var i = 0; i<individual_words; i++){
var colour = colour_options[Math.floor(Math.random()*colour_options.length)]
var span = "<span style='background_color: " + colour + ";'>" + individual_words[i] + "</span>"

spans.push(span);
}
all_words.innerHTML = spans.join(" ");