Does CSS have a :blur selector (pseudo-class)?

Question

There is no :blur pseudo-class in CSS.

The dynamic pseudo-classes, like other pseudo-classes and in fact all other selectors, represent states; they do not represent events or transitions between states in terms of the document tree. To wit: the :focus pseudo-class represents an element that is in focus; it does not represent an element that has just received focus, nor does there exist a :blur pseudo-class to represent an element that has just lost focus.

Similarly, this applies to the :hover pseudo-class. While it represents an element which has a pointing device over it, there is neither a :mouseover pseudo-class for an element that has just been pointed to nor a :mouseout pseudo-class for an element that has just been pointed away from.

If you need to apply styles to an element that is not in focus, you have two choices:

1. Use :not(:focus) (with less browser support):

   input:not(:focus), button:not(:focus) {
       /* Styles for only form inputs and buttons that do not have focus */
   }
   

2. Declare a rule that applies to any element regardless of its focus state, and override for elements that have focus:

   input, button {
       /* Styles for all form inputs and buttons */
   }
   
   input:focus, button:focus {
       /* Styles for only form inputs and buttons that have focus */
   }
   

No, CSS has no blur pseudo-selector, presumably because blur is more of an event than a state. (It would be unclear when something should lose its blur state).

All regular selectors are by default not focussed. So you don't need a special blur selector.

These are the selectors by precedence.

.myButton
.myButton:hover
.myButton:focus
.myButton:active

Use the general transition to set the blur transition.

.example {
  transition-property: opacity;
  transition-duration: 2s; /* This will happen after the hover state and can also be used for consistency on the overall experience */
  opacity: 0;
}
.example:hover {
  opacity: .8;
  transition-duration: .3s;
  transition-delay: .1s;
}