index.css

* {
  box-sizing: border-box;
}

body {
  display: flex;
  flex-direction: column;
  align-items: center;
}

#books {
  display: flex;
  justify-content: center;
  flex-direction: column;
  width: 70%;
  border: 4px solid black;
  margin-bottom: 12px;
}

#books > div {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 0 12px;
}

#books > div:nth-child(odd) {
  background-color: #ddd;
}

#books > div > p {
  margin: 8px 0;
}

.underline {
  width: 50px;
  height: 4px;
  background-color: black;
  margin: 1rem;
}

form {
  width: 50%;
  display: flex;
  flex-direction: column;
  justify-content: center;
}

form > *:not(:nth-child(1)) {
  margin: 0.5rem;
  font-size: 1rem;
  padding: 4px;
  border: 1px solid #000;
}

form button {
  align-self: flex-end;
  padding: 4px 8px !important;
  background-color: #fff;
}

h2 {
  font-size: 2rem;
  text-align: center;
}

form h2 {
  margin-top: -200px;
}

header {
  display: flex;
  flex-direction: row;
  width: 95vw;
  justify-content: space-between;
  border: 2px solid #000;
  padding: 0 1rem;
}

header h1 {
  font-size: 1.5rem;
}

header > nav {
  list-style: none;
  display: flex;
  flex-direction: row;
  align-items: center;
}

header > nav > a {
  text-decoration: none;
  color: #000;
  padding: 12px;
}

header > nav > a.active {
  color: blue;
}

header > nav > a:nth-child(2) {
  border-left: 1px solid #000;
  border-right: 1px solid #000;
}

#date {
  align-self: flex-end;
  margin-right: 1rem;
  margin-top: 0.5rem;
  margin-bottom: 0.5rem;
}

footer {
  display: flex;
  flex-direction: row;
  width: 95vw;
  justify-content: flex-start;
  border: 2px solid #000;
  padding: 0 1rem;
}

.all-books {
  width: 100%;
  align-items: center;
  display: flex;
  flex-direction: column;
  overflow-y: auto !important;
}

.all-books,
form,
#contact {
  overflow-y: hidden;
  height: calc(96vh - 168px);
}

#contact {
  padding: 5rem 0 0 0;
  font-size: 1.2rem;
}

#contact > p:nth-child(1) {
  margin-top: 3rem;
}

.hidden {
  display: none;
}