HTML is responsible for the structure of the page. But if you load a page and everything seems to look all wrong or it just looks plain, then you may have been loading an HTML page without the CSS. The HTML outlines the structure, but the CSS determines the style and design of the page.
CSS stands for Cascading Style Sheets. Essentially with CSS, you can choose an HTML element, or specific set of tags or related elements and say how you want to style them. When you say how you want to style them, you can change the font, the color, the size, the margins (the spacing around the elements), and many more things.
For example, if you wanted to say that all text within paragraphs should be red, you’d write a CSS rule like this:
p {
color: red;
}
A CSS rule shows which elements you want to select. And then what things to change about them. So when you say “color: red” - you are setting the "color" property to have the value "red.""
Look at a site with css text at readwritecodebook.com/chapter3/css.html.