How to change the background colors of all <em> elements

Question

I am trying to change the background colors of all italized text, instead of using a span on every single word through the paragraph. It says <em> next to the italized text. I have tried

$(".em").css({
    "background-color":"#d9f9f9",
});

or/and tried this:

var elem=document.getElementByTagName(em)[1];
elem.style.backgroundColor='#d9f9f9';

Answer 1

See querySelectorAll:

Notices this method return an array, so we should loop it:

var emList = document.querySelectorAll('em');

[].forEach.call(emList , function(em) {
  // do whatever
  em.style.color = "red";
});

Answer 2

Your first suggestion says ".em" where it should say "em". Your seconds suggestion says em where it should say "em".