Some of the most important CSS properties:

Box Model: The box model properties (width, height, padding, border, and margin) define the size and spacing of elements on a page.

Display: The display property determines how an element is displayed on the page, such as as a block or inline element.

Text Style: The text style properties (font-size, font-family, color, text-align, etc.) control the appearance of text within an element.

Positioning: The positioning properties (position, top, bottom, left, right) control the position of elements on the page.

Flexbox: Flexbox is a layout mode that makes it easy to create flexible and responsive designs by defining how elements should be positioned along a main axis and a cross axis.

Grid: Grid is a two-dimensional layout system that allows you to create grid-based designs with rows and columns.

Backgrounds and Borders: The background and border properties (background-color, background-image, border, border-radius) control the appearance of backgrounds and borders of elements.

Transitions and Animations: Transitions and animations (transition, animation) add movement and visual effects to elements on a page.

Media Queries: Media queries allow you to create responsive designs by applying different styles based on the size of the viewport or other criteria.

These are just a few of the most important CSS properties. However, there are many more that you can use to create complex and sophisticated designs for the web.