<button class="button">Mouse over me</button>
body {
  display: flex;
  min-height: 100vh;
  justify-content: center;
  align-items: center;
}

.button {
  font-size: 3em;
  font-family: inherit;
  border: none; 
  background-color: #33ae74;
  padding: 0.5em 0.75em;
  transition: background-color 0.5s ease-out;
}

.button:hover {
  background-color: #1ce;
  transition-duration: 2s;
}

External CSS

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External JavaScript

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