css transition in code example

Example 1: display transition css

div {
  background-color: blue;
  padding: 40px;
  color: white;
  cursor: pointer;
  transition: all .1s ease;
}

.hidden {
  visibility: hidden;
  opacity: 0;
  max-height: 0%;
}

.hidden:hover {
  visibility: visible;
  opacity: 1;
  max-height: 1000px;
}
<div class="hidden"></div>

Example 2: css transform transition

.selector {
  transition: transform 1s;
}

Example 3: learn css animations transform

Read this comprehensive article about CSS animation transform property. 
It also has many useful examples that help you in best way.

https://medium.com/swlh/learn-css-transform-animation-zero-to-hero-6a2a643bd56b

Example 4: css opacity transition

div {
  transition: opacity seconds;
}