Why we use CSs language, html have all features.

Question

I can not understand, why we learn CSS , we have already html language.

Answer 1

CSS is very different from HTML. While HTML structures the page to have its articles and headings and all, CSS is what puts them in their places and gives them color, fonts, and other things it needs to look nice.
When you use the style attribute or the <style> tag, you're using CSS anyway. Yes, you can place all your CSS inside the HTML, but it's more convenient to place it in its own file and import it. That way, you can use it on dozens of HTML pages at once, and so change them all at once.

Answer 2

if you have 100 link in your html structure
how much time you need to set the color blue for all link ?
<a href="#" style="color:blue;"> </a>
ok you can write style inline it in html , so if you want to change this color do you need to change every link style ?

with css you just do it one time
a{color:blue;}

this is a double answer for why using CSS and how using CSS ;)