body {
  font-family: Arial, sans-serif;
  margin: 0;
  padding: 0;
  display: flex;
  min-height: 100vh;
  flex-direction: column;
}

header {
  background-color: #333;
  color: #fff;
  padding: 1rem;
}

nav {
  width: 50%;
  margin: 0 auto;
  text-align: center;
}  

nav ul {
  list-style: none;
  margin: 0;
  padding: 0;
  display: flex;
}

nav li {
  margin-right: 20px;
}

nav a {
  color: #fff;
  text-decoration: none;
  position: relative;
}

nav a::before {
  content: "";
  display: block;
  position: absolute;
  bottom: -5px;
  left: 50%;
  width: 0;
  height: 2px;
  background-color: #fff;
  transition: all 0.3s;
}

nav a:hover {
  transform: scale(1.1);
}

nav a:hover::before {
  width: 50%;
  left: 25%;
}

main {
  padding: 20px;
  flex: 1;
  text-align: left;
  margin-left: 20%;
  margin-right: 30%;
  display: flex;
  flex-wrap: wrap;
  overflow-y: hidden;
  height: 100%;
}

.main-left,
.main-right {
  flex-basis: 20%;
  overflow-y: auto;
  padding: 0 10px;
}

.main-left {
  order: 0;
}

.main-right {
  order: 2;
}

.main-middle {
  flex-basis: 60%;
  overflow-y: auto;
  padding: 0 10px;
  order: 1;
}

.container {
  max-width: 1200px;
  margin: 0 auto;
  padding: 20px;
}

.container {
  width: 80%;
  margin: 0 auto;
}

#top-btn {
  position: fixed;
  bottom: 20px;
  right: 20px;
  background-color: #333;
  color: #fff;
  padding: 10px 20px;
  border: none;
  border-radius: 5px;
  cursor: pointer;
}

#top-btn a {
  color: #fff;
  text-decoration: none;
}

footer {
  background-color: #333;
  color: #fff;
  padding: 1rem;
  text-align: center;
}