:root {
  --white: #fffbfb;
  --black: #0d1117;
  --semi-black: #0f172a;
  --grey: #f0eef1;
  --light-green: #60b564;
  --dark-green: #388e3c;
  --light-red: #f44336;
  --border-radius: 10px;
  --spacing-xs: 5px;
  --spacing-sm: 10px;
  --spacing-md: 15px;
  --spacing-lg: 20px;
  --spacing-xl: 40px;
  --container-width: 1200px;
  --shadow: rgba(0, 0, 0, 0.16) 0px 1px 4px;
}

/* Reset CSS */
*::before,
*::after,
* {
  padding: 0;
  margin: 0;
  text-decoration: none;
  box-sizing: border-box;
}

html {
  position: relative;
  min-height: 100%;
}

body {
  background-color: var(--black);
  color: var(--white);
  font-family: "Poppins", sans-serif;
  font-size: 15px;
  font-weight: 500;
  word-wrap: break-word;
  margin-bottom: 100px;
}

/* Utilities */

.container {
  max-width: var(--container-width);
  padding: var(--spacing-lg);
  margin: 0 auto;
}

.container h1 {
  text-align: center;
  width: 100%;
}

.btn {
  padding: var(--spacing-sm);
  border-radius: var(--border-radius);
  transition: filter 0.15s ease-in-out;
  cursor: pointer;
}

.btn:hover {
  filter: brightness(90%);
}

.btn:active {
  transform: translateY(-1px);
  box-shadow: 0 5px 10px rgba(0, 0, 0, 0.2);
}

.btn-light-green {
  background-color: var(--light-green);
  font-size: 18px;
}

.btn-light-red {
  background-color: var(--light-red);
}

.btn-add {
  font-size: 24px;
  background-color: var(--grey);
}

/* header */
header {
  background-color: var(--semi-black);
  border-bottom: 1px solid #f0eef1;
}

header .container {
  display: flex;
  align-items: center;
  justify-content: space-between;
}

/* main */

.main {
  text-align: left;
  margin-left: var(--spacing-xl);
  margin-right: var(--spacing-xl);
  margin-top: var(--spacing-xl);
}

.books-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
  gap: var(--spacing-xl);
  margin-top: var(--spacing-xl);
}

.book-card {
  display: flex;
  flex-direction: column;
  justify-content: space-between;
  font-size: 15px;
  gap: var(--spacing-lg);
  padding: var(--spacing-lg);
  border-radius: var(--border-radius);
  background-color: #222a74;
  box-shadow: var(--shadow);
  line-height: 1.2;
  text-align: center;
}

.button-group {
  display: flex;
  flex-direction: column;
  gap: var(--spacing-lg);
}

.col {
  width: 100%;
}

/* footer */

.footer {
  width: 100%;
  position: absolute;
  bottom: 0;
  width: 100%;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: var(--spacing-lg);
}

/* modal */

.modal {
  z-index: 1;
  position: fixed;
  left: 50%;
  top: 50%;
  width: 500px;
  height: 500px;
  padding: var(--spacing-lg);
  border-radius: var(--border-radius);
  background-color: var(--semi-black);
  text-align: center;
  transform: translate(-50%, -50%) scale(0);
  transition: 0.2s ease-in-out;
}

.modal.active {
  transform: translate(-50%, -50%) scale(1);
}

.modal h3 {
  margin-bottom: var(--spacing-md);
  font-size: 30px;
}

.input {
  border-radius: var(--border-radius);
  width: 100%;
  padding: var(--spacing-md);
  margin-bottom: var(--spacing-xl);
}

.is-read {
  display: flex;
  gap: var(--spacing-md);
  align-items: center;
  margin-bottom: var(--spacing-md);
}

.checkbox {
  width: 20px;
  height: 20px;
  accent-color: var(--white);
  margin-top: var(--spacing-sm);
}

.overlay {
  position: fixed;
  top: 0;
  left: 0;
  display: none;
  width: 100%;
  height: 100%;
  background-color: rgba(0, 0, 0, 0.5);
}

.overlay.active {
  display: block;
}

.close-modal-btn {
  cursor: pointer;
  position: absolute;
  right: -10px;
  top: -10px;
}

.submit-btn {
  width: 100%;
}

/* loading ring */

/* media queries */
@media (max-width: 480px) {
  .header .container {
    flex-direction: column;
    gap: var(--spacing-md);
    padding-top: var(--spacing-sm);
  }

  .main {
    margin-top: var(--spacing-md);
  }

  :root {
    --spacing-xl: 20px;
  }

  .modal {
    width: 300px;
    height: 400px; 
  }
}