/* element selector */
body {
  font-family: Arial, sans-serif;
  background-color: #f7f9fb;
  color: #222;
  margin: 40px;
}

/* Class Selector */
.section-title {
  color: #1a73e8;
  border-bottom: 2px solid #1a73e8;
  padding-bottom: 4px;
}

.intro {
  font-size: 1.1em;
  background-color: #eef4ff;
  padding: 10px;
  border-radius: 5px;
}

/* ID Selector */
#main-title {
  text-align: center;
  color: #b22222;
}

#diagram {
  display: block;
  margin: 20px auto;
  border: 3px solid #aaa;
  border-radius: 10px;
}

/* Additional example */
.author {
  font-weight: bold;
  color: #006400;
}