The main difference between the two pseudoclasses is that the `:focus` pseudoclass is applied when the user starts interacting with the element, while the `:active` pseudoclass is applied when the user finishes interacting with the element. For example, if you have a button that changes color when it is focused, the `:focus` pseudoclass will be applied when the user tabs to the button or clicks on it with the mouse. The `:active` pseudoclass will not be applied until the user actually clicks on the button and starts to press down. The `:focus` and `:active` pseudoclasses are both used to style elements in different states, but they have different meanings. 1. The `:focus` pseudoclass is used to style an element when it is in focus. This means that the element is currently receiving input from the user, either through a keyboard or a mouse. 2. The `:active` pseudoclass is used to style an element when it is being activated by the user. This means that the user is currently clicking or pressing on the element. Here is an example of how to use the `:focus` and `:active` pseudoclasses in CSS: 

button:focus {
  background-color: yellow;
  color: black;
}

button:active {
  background-color: red;
  color: white;
}
This code will make a button change color from yellow to red when it is clicked. The `:focus` pseudoclass will be applied when the user tabs to the button or clicks on it with the mouse, and the `:active` pseudoclass will be applied when the user actually clicks on the button and starts to press down. It is important to note that not all elements can be focused. Only elements that are able to receive input from the user, such as buttons, input boxes, and text areas, can be focused. Also, the `:active` pseudoclass is not supported by all browsers. For example, it is not supported by the mobile Safari browser. Conclusion: In general, the `:focus` pseudoclass is a more reliable way to style elements that are being interacted with by the user. The `:active` pseudoclass should only be used if you need to style an element in a specific way when it is being activated by the user.