Diffirence from ID and Class

Question

Class selectors work in a similar way. The major difference is that IDs can only be applied once per page, while classes can be used as many times on a page as needed.

If will use this cod , it work the same. Why guys?
The HTML:
<div>
<p id="first">This is a paragraph</p>
<p> This is the second paragraph. </p>
</div>
<p id="first"> This is not in the intro section</p>
<p> The second paragraph is not in the intro section. </p>

The CSS:
#first {font-size: 200%;}

Answer 1

Take note that HTML is a markup language.

Unlike most programming languages, nothing stops you from digging yourself into a hole in HTML.

It obviously wrong to have duplicate global attribute (id) but the browser will still try its best to parse it. So please don't do it. 😉

Answer 2

ID is used to get a specific tag item while class is for a group of tags.
Depending of your purposes you may prefer one or the other.

Answer 3

this will be more troublesome when javascript access DOM

examples:

document.getElementById("first") //error occur

Answer 4

the differents in specificity of selectors
https://developer.mozilla.org/uk/docs/Web/CSS/Specificity