text: /* variable, operator */
  body {
    font: 80% Helvetica, sans-serif;
    color: #333333; }
  
  /* nesting */
  nav ul {
    margin: 0;
    padding: 0;
    list-style: none; }
  nav li {
    display: inline-block; }
  nav a {
    display: block;
    padding: 6px 12px;
    text-decoration: none; }
  
  /* mixin */
  .box {
    -webkit-border-radius: 10px;
    -moz-border-radius: 10px;
    -ms-border-radius: 10px;
    -o-border-radius: 10px;
    border-radius: 10px; }
  