<div class="box">
  I use the standard box model.
  </div>

<div class="box box2">
  I use the alternate box model.
  </div>

body {
  padding: 20px;
  font: 1em Helvetica Neue, Helvetica, Arial, sans-serif;
}

p {
  margin: 0 0 1em 0;
}

.box {  
  border: 5px solid rgb(111,41,97);
  border-radius: .5em;
  padding: 20px;
  width: 200px;
  margin-bottom: 2em;
}

.box2 {
  box-sizing: border-box;
}