Shake input field when invalid, using CSS

One of the most common feedback animations is shaking an input field when the user enters invalid data. Luckily, HTML and CSS have just the right tools to help you create this effect.

Starting with the HTML, we'll need to use the pattern attribute to define the regular expression which the input's value must match. This will trigger the :invalid pseudo-class when the input is invalid.

Then, using @keyframes, we can define a shake animation that uses the margin-left property to move the element back and forth. Finally, we can use the :invalid pseudo-class to apply the animation to the element, making it shake when the user enters invalid data.

 <input type="text" placeholder="Letters only" pattern="[A-Za-z]*" />

input:invalid {
  animation: shake 0.2s ease-in-out 0s 2;
}

@keyframes shake {
  0% {
    margin-left: 0rem;
  }
  25% {
    margin-left: 0.5rem;
  }
  75% {
    margin-left: -0.5rem;
  }
  100% {
    margin-left: 0rem;
  }
}

https://codepen.io/chalarangelo/pen/dyxorLK