Cascading Style Sheets (CSS) is a style sheet language used to give a website a visually appealing look by describing how HTML elements should be displayed on a screen, in print, or in other media.

CSS provides web developers with the ability to define the presentation of HTML elements, such as fonts, colors, layout, and sizing. It allows developers to separate the presentation of a web page from its informational content, making it easier to manage and modify the visual appearance of a website.

Here is an example of a CSS code block that changes the font style of all h1 elements on a web page:

h1 {

font-family: Arial, sans-serif;

font-weight: bold;

font-size: 2em;

color: #333;

}

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In this example, the h1 selector is used to target all h1 elements on a web page. The CSS code block then specifies the font family, font weight, font size, and color for these elements