Confusion in HTML "Tables" Interactive Lesson

Hello, i am very new to coding and have been taking the “Introduction to HTML Course”

I have finished the first portion of the html lessons called “Learn HTML: Elements and Structure”
and then i went on to the second portion called “Learn HTML: Tables” and now i’m doing the first lesson in the that portion which is called “Tables Interactive Lesson” But the lesson starts talking about “CSS” and “Cells” and stuff the first portion never went over at all, it continues to refer that i learned stuff about CSS in the past, but i never saw it even be mentioned until this lesson. Am i making a mistake? did i do the courses in the wrong order? or am i suppose to know this CSS stuff from the start? If anyone could answer this question, it would be greatly appreciated. because i honestly though you were supposed to the full HTML course and then Move on to CSS.

The question does seem to come up with regular frequency so I doubt you have missed anything. Likely some order got switched around with revision and new iterations of the course material. Not to worry.

Click the tab that reads, ‘style.css’

It may look like Greek, but just take it in. We only need to make one minor addition.

If you look down the left side of the style sheet you will see what look like HTML tags but without the carats.

h1

as opposed to,

<h1>

That is known as a selector for the H1 type of element. The segment within the curly braces that follows the selector is known as the declaration block. It contains a list of property declarations which break down as follows:

property-name: value;

Following this pattern, we can create a selector rule that will apply to both TH and TD like so, (note the comma, which is important, here)

th, td {
    font-size: 18px;
}

If you scroll down the style sheet until you find the rule for th and after its closing curly brace insert a blank line and paste in the above selector rule. Adjust as directed to have the correct property and value. I’m going from memory.

That should be all you need to do to move on from this lesson. CSS will come up in greater detail, so don’t get hung up.