*,
*::after,
*::before {
  box-sizing: border-box;
}
body,
p,
.container {
  margin: 0;
  padding: 0;
}
body {
  background: gray;
  line-height: 1.5em;
}
.container {
  background: whitesmoke;
  width: 70%;
  padding: 1em 2em;
  margin: 2em auto;
}
h1 {
  font-size: 18px;
}
.section1 {
  color: green;
  padding: 0.5em 2em;
  border: 5px solid green;
  width: 70%;
  margin: 2em auto;
}

.section1 p {
  font-size: 14px;
}

.section2 {
  color: red;
  padding: 0.5em 2em;
  /* margin: 2em 0.5em; */
}
.section2 h2,
.section2 p,
.section2 ul li,
.section2 h4 {
  font-size: 14px;
}
.css-example {
  background: gainsboro;
  padding: 0.5em 1em;
  margin: 1em 5em;
}
.css-example div {
  width: 200px;
  background: #00008b;
  padding: 1em 2em;
  margin: 1em;
}
.section3 {
  width: 70%;
  color: blue;
  padding: 0.5em 2em;
  border-right: 3px double blue;
  border-left: 3px double blue;
  margin: 0 2em;
}
.section3 p,
.section3 h3 {
  font-size: 14px;
}