index.css

@import url('https://fonts.googleapis.com/css2?family=Berkshire+Swash&display=swap');
@import url('https://fonts.googleapis.com/css2?family=Raleway:ital,wght@0,100;0,200;0,300;0,400;0,500;0,600;0,700;0,800;0,900;1,100;1,200;1,300;1,400;1,500;1,600;1,700;1,800;1,900&display=swap');

* {
  font-family: 'Raleway', sans-serif;
  text-decoration: none;
}

:root {
  --color-primary: #2c5690;
  --color-secondary: #758bc1;
  --color-third: #d8f9fd;
}

body {
  padding: 0;
  margin: 0;
  height: 100vh;
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
  background-color: rgba(238, 238, 238, 0.702);
  background-blend-mode: saturation;
  background-image: url('./bg.jpg');
  background-repeat: no-repeat;
  background-position: center;
  background-size: cover;
  backdrop-filter: blur(20px);
}

.alert {
  position: fixed;
  height: 36%;
  width: 100%;
  display: flex;
  justify-content: center;
  align-items: center;
  text-align: center;
  font-size: 30px;
  font-weight: 500;
  background-blend-mode: multiply;
}

.alert-danger {
  background-color: #731010e0;
  color: #fff;
}

.alert-success {
  background-color: #24a379e0;
  color: #fff;
}

#date {
  padding: 0;
  margin: 2em;
  font-size: 16px;
  font-weight: 300;
  text-align: center;
  letter-spacing: 2px;
}

#navbar {
  display: flex;
  justify-content: center;
  align-items: center;
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  background-color: #ebf2f3;
  box-shadow: 1px 2px 10px rgb(39 42 50);
}

#nav-container,
#footer-cont {
  display: flex;
  justify-content: space-between;
  width: 90%;
  max-width: 900px;
}

#nav-container h1 {
  font-family: 'Berkshire Swash', cursive;
  font-size: 36px;
  background-image: linear-gradient(90deg, var(--color-primary), var(--color-secondary), var(--color-third));
  background-clip: text;
  -webkit-background-clip: text;
  color: transparent;
  width: 50%;
}

#nav-links {
  display: flex;
  justify-content: space-around;
  margin: 0;
  padding: 0;
  width: 50%;
}

#list-btn,
#add-btn,
#contact-btn {
  display: flex;
  text-align: center;
  justify-content: center;
  align-items: center;
  font-weight: 600;
  font-size: 18px;
  list-style: none;
  cursor: pointer;
  text-transform: uppercase;
}

#nav-links li:hover {
  color: var(--color-primary);
}

#nav-links li.active {
  color: var(--color-primary);
}

#add,
#list,
#contact {
  display: none;
  padding: 0;
  flex-wrap: wrap;
  justify-content: center;
  align-items: center;
  width: 60%;
  max-width: 600px;
}

#contact {
  text-align: center;
  font-size: 26px;
  color: var(--color-secondary);
}

#contact ul {
  text-align: left;
  font-size: 18px;
  color: var(--color-primary);
}

#add h2,
#list h2,
#contact h2 {
  padding: 0;
  margin: 1rem 0;
  width: 80%;
  text-align: center;
  font-size: 40px;
  color: var(--color-primary);
}

#add.show {
  display: flex;
}

#list {
  display: none;
}

#list.show {
  display: flex;
}

#contact.show {
  display: flex;
}

div#book-list {
  width: 80%;
  border: 2px solid #555;
}

div#book-list .book:nth-child(even) {
  background-color: var(--color-secondary);
}

div.book {
  display: flex;
  padding: 0;
  width: 100%;
  justify-content: space-between;
  align-items: center;
  background-color: var(--color-third);
  font-size: 14px;
}

.book h3 {
  padding: 0 0.5em;
}

.book h3 + h3 {
  font-style: italic;
  font-weight: 400;
  font-size: 14px;
}

.remove-btn {
  cursor: pointer;
  padding: 0.25em 0.5em;
  margin: 0 0.5em;
  background-color: var(--color-secondary);
  color: #eee;
  font-size: 1.25em;
  border-radius: 6px;
}

.remove-btn:hover {
  background-color: var(--color-primary);
}

#book-form {
  width: 80%;
  display: flex;
  flex-direction: column;
  align-items: center;
}

#book-form input {
  width: 90%;
  margin: 0.5em 0 0;
  padding: 0 0.5em;
  border: 3px solid var(--color-third);
  font-size: 1.5em;
  border-radius: 6px;
}

#book-form input:focus {
  border: 3px solid var(--color-primary);
}

#book-form button {
  width: 60px;
  cursor: pointer;
  padding: 0.25em 0.5em;
  margin: 1em;
  background-color: var(--color-primary);
  color: #eee;
  font-size: 1em;
  border-radius: 6px;
}

#book-form button:hover {
  background-color: var(--color-third);
}

footer {
  display: flex;
  position: fixed;
  bottom: 0;
  left: 0;
  width: 100%;
  justify-content: center;
  background-color: var(--color-primary);
  color: #fff;
}