main.css

/****************************************
* General
****************************************/
html {
  font-family: Sans-Serif;
  text-align: center;
}

.container {
  width: 600px;
  margin:auto;
}

[class$=demo]{
  border: 1px solid silver;
  min-height: 200px;
  margin: 5px;
  box-shadow: 2px 2px 4px darkgrey;
  border-radius: 2px;
}

/****************************************
* Transform
****************************************/
.transform-demo > h3 {
  vertical-align: top;
  width: 30%;
  margin: 5px  auto;
  display: inline-block;

}
/****************************************
* Transition
****************************************/

.transition-demo img {
  width: 200px;
  height: 200px;
}

.cards {
  display: flex;
  justify-content: space-around;
}

a {
  opacity: .5;
  text-decoration: none;
  color: salmon;
}