index.css

*{
    margin: 0;
    list-style: none;
    text-decoration: none;
    color: #000;
    box-sizing: border-box;
}

body {
    font-family: Arial, Helvetica, sans-serif;
    font-size: 1.2rem;
    padding: 10px;
}

header {
    height: 10vh;
    text-align: center;
   display: flex;
   justify-content: center;
}

header nav {
    display: flex;
    text-align: center;
    padding: 10px;
    border: 1px solid #000;
   justify-content: space-between;
    width: 100%;
    align-items: center;
}

header nav ul {
    display: flex;
    gap: 20px;
}

#date {
    float: right;
}

/* booklist section */
#book-list-section {
    display: flex;
    justify-content: center;
    align-items: center;
      margin-bottom: 20px;
      margin-top: 20px;
}

.content {
    width: 70%;
}

.content h1 {
    display: flex;
    flex-direction: column;
    align-items: center;
}

#book-list {
   display: flex;
   flex-direction: column;
   gap: 10px;
   border: 1px solid #000;
    padding: 0;
}

.book-list-item {
   background-color: #eee;
   padding: 10px;
}

.book-list-item:nth-child(even) {
   background-color: #fff;
   padding: 10px;
}

.remove,
#btn {
    float: right;
    padding: 5px;
    font-weight: 700;
    border: 2px solid #000;
}


/* addbook-section */
#add-book-section {
    display: none;
    justify-content: center;
    align-items: center;
      margin-bottom: 20px;
      margin-top: 20px;
}

form {
    display: flex;
    flex-direction: column;
    gap: 10px;
    margin-bottom: 10px;
    margin-top: 10px;
    width: 30%;
}

form > input {
    padding: 10px;
}

form > input::placeholder {
    font-weight: 500;
    color: #000;
}


/* 
.alert-danger {
    background-color: red;
    color: #fff;
} */

/* contact-section */
#contact-section{
    display: none;
    flex-direction: column;
    gap: 10px;
    align-items: center;
    margin-top: 20px;
}

footer {
    position: absolute;
    bottom: 0;
    width: 98%;
    padding: 10px;
   border: 1px solid #000;
   margin-bottom: 10px;
}