solution.css

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

a {
  text-decoration: none;
  color: #ffffff;
}
header {
  width: 100%;
  padding: 15px;
  background: #000000;
  color: white;
  text-align: center;
  position: sticky;
  top: 0;
}
nav {
  background: #1c641c;
  height: 50px;
  width: 100%;
  padding: 15px;
}
ul {
  list-style: none;
  display: flex; /* 금요일에 배울 내용입니다! */
  justify-content: flex-end;
}

ul > li {
  margin: 0px 5px;
}

article {
  width: 100%;
}
section {
  width: 100%;
  padding: 15px;
}
section:nth-child(1) {
  background: #973618;
  height: 500px;
}
section:nth-child(2) {
  background: orange;
  height: 500px;
}
section input {
  display: block;
  border: 0px;
  padding: 20px;
  border-radius: 3px;
  margin-top: 5px;
}
footer {
  background-color: #829967;
  width: 100%;
  padding: 15px;
  text-align: center;
}