The opacity CSS property is used to control the transparency or opacity of an element and its content. It specifies the degree to which the element is visible or hidden.

The opacity property accepts values ranging from 0.0 to 1.0, where 0.0 represents completely transparent (invisible) and 1.0 represents fully opaque (fully visible).

Here’s an example:

.element {
  opacity: 0.5;

In this example, the .element class sets the opacity of the element and its content to 0.5, making it partially transparent. This means the element will be 50% visible, allowing the background or underlying elements to be partially seen through it.

You can adjust the opacity value to create various transparency effects. For example, setting opacity: 0.2 would make the element highly transparent, while opacity: 0.8 would make it mostly opaque with some transparency.

It’s important to note that the opacity property affects the entire element and its content. If you only want to change the transparency of the element’s background color or text, you can use the rgba() color notation instead.

The opacity property is commonly used to create visual effects, such as fading elements in and out or overlaying elements with transparency. It provides control over the visibility and transparency of elements, enhancing the overall design and user experience.