:root {
  --primary-color: #111827;
  --secondary-color: #6b7280;
  --background-color: #f8fafc;
  --surface-color: #ffffff;
  --border-color: #e5e7eb;
  --text-color: #1f2937;
}

* {
  box-sizing: border-box;
}

html {
  min-height: 100%;
}

body {
  min-height: 100vh;
  margin: 0;
  font-family: Arial, sans-serif;
  background-color: var(--background-color);
  color: var(--text-color);
  line-height: 1.5;
}

/* =========================
   HEADER
   ========================= */

header {
  background-color: var(--surface-color);
  border-bottom: 1px solid var(--border-color);
  position: sticky;
  top: 0;
  z-index: 100;
}

header nav {
  max-width: 1200px;
  margin: 0 auto;
  padding: 1rem 1.5rem;
  display: flex;
  align-items: center;
  gap: 2rem;
}

header nav > a {
  order: 1;
  color: var(--primary-color);
  font-size: 1.25rem;
  font-weight: 700;
  text-decoration: none;
  white-space: nowrap;
}

header nav > a:hover {
  color: #374151;
}

#mobile-menu {
  display: contents;
}

#product-search {
  order: 2;
  flex: 1;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

#product-search label {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

#product-search input {
  width: 100%;
  max-width: 500px;
  padding: 0.7rem 0.9rem;
  border: 1px solid var(--border-color);
  border-radius: 6px;
  background-color: var(--surface-color);
  color: var(--text-color);
  outline: none;
}

#product-search input:focus {
  border-color: var(--primary-color);
}

#product-search button {
  padding: 0.7rem 1rem;
  border: none;
  border-radius: 6px;
  background-color: var(--primary-color);
  color: #ffffff;
  font-weight: 600;
  cursor: pointer;
  transition: background-color 0.2s ease;
}

#product-search button:hover {
  background-color: #374151;
}

#header-actions {
  order: 3;
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

#cart-link {
  color: var(--text-color);
  text-decoration: none;
  font-size: 0.95rem;
  font-weight: 600;
  transition: color 0.2s ease;
}

#cart-link:hover {
  color: #6b7280;
}

#auth-navigation {
  order: 4;
  display: flex;
  align-items: center;
  gap: 1.25rem;
}

#auth-navigation a,
#auth-navigation button {
  color: var(--text-color);
  text-decoration: none;
  font-size: 0.95rem;
  font-weight: 600;
}

#auth-navigation a {
  transition: color 0.2s ease;
}

#auth-navigation a:hover,
#auth-navigation button:hover {
  color: #6b7280;
}

#auth-navigation button {
  padding: 0;
  border: none;
  background: none;
  cursor: pointer;
}

#menu-toggle {
  display: none;
  min-width: 42px;
  min-height: 42px;
  padding: 0.5rem;
  border: 1px solid var(--border-color);
  border-radius: 6px;
  background-color: var(--surface-color);
  color: var(--text-color);
  font-size: 1.25rem;
  line-height: 1;
  cursor: pointer;
  transition:
    background-color 0.2s ease,
    border-color 0.2s ease;
}

#menu-toggle:hover {
  background-color: #f3f4f6;
  border-color: #9ca3af;
}

/* =========================
   MAIN
   ========================= */

main {
  max-width: 1200px;
  margin: 0 auto;
  padding: 3rem 1.5rem;
}

main section {
  width: 100%;
}

main section h1 {
  margin-bottom: 2rem;
  color: var(--primary-color);
  font-size: 2rem;
  line-height: 1.2;
}

/* =========================
   PRODUCT DETAILS
   ========================= */

#product-details {
  display: grid;
  grid-template-columns: minmax(0, 1.1fr) minmax(0, 0.9fr);
  column-gap: 3rem;
  row-gap: 1rem;
  padding: 2rem;
  background-color: var(--surface-color);
  border: 1px solid var(--border-color);
  border-radius: 8px;
}

/* =========================
   PRODUCT NAME
   ========================= */

#product-details h2 {
  grid-column: 2;
  grid-row: 1;
  margin: 0 0 0.5rem;
  color: var(--primary-color);
  font-size: 1.7rem;
  line-height: 1.3;
}

/* =========================
   PRODUCT IMAGE
   ========================= */

#product-details img {
  grid-column: 1;
  grid-row: 1 / span 7;
  width: 100%;
  height: 430px;
  object-fit: cover;
  border: 1px solid var(--border-color);
  border-radius: 6px;
}

/* =========================
   DESCRIPTION
   ========================= */

#product-details > p:nth-of-type(1) {
  grid-column: 2;
  grid-row: 2;
  margin: 0;
  color: var(--secondary-color);
  font-size: 0.95rem;
  line-height: 1.7;
}

/* =========================
   PRICE
   ========================= */

#product-details > p:nth-of-type(2) {
  grid-column: 2;
  grid-row: 3;
  margin: 0.5rem 0 0;
  color: var(--text-color);
  font-size: 1.3rem;
  font-weight: 700;
}

/* =========================
   STOCK
   ========================= */

#product-details > p:nth-of-type(3) {
  grid-column: 2;
  grid-row: 4;
  margin: 0;
  color: var(--secondary-color);
  font-size: 0.85rem;
}

/* =========================
   QUANTITY
   ========================= */

#product-details label {
  grid-column: 2;
  grid-row: 5;
  align-self: end;
  margin-bottom: 0.4rem;
  color: var(--text-color);
  font-size: 0.85rem;
  font-weight: 600;
}

#product-quantity {
  grid-column: 2;
  grid-row: 6;
  width: 100%;
  max-width: 140px;
  padding: 0.7rem 0.8rem;
  border: 1px solid var(--border-color);
  border-radius: 6px;
  background-color: var(--surface-color);
  color: var(--text-color);
  font-family: inherit;
  font-size: 0.95rem;
  outline: none;
}

#product-quantity:focus {
  border-color: var(--primary-color);
}

/* =========================
   ADD TO CART
   ========================= */

#product-details > button {
  grid-column: 2;
  grid-row: 7;
  width: 100%;
  padding: 0.8rem 1rem;
  border: none;
  border-radius: 6px;
  background-color: var(--primary-color);
  color: #ffffff;
  font-family: inherit;
  font-size: 0.95rem;
  font-weight: 600;
  cursor: pointer;
  transition:
    background-color 0.2s ease,
    opacity 0.2s ease;
}

#product-details > button:hover {
  background-color: #374151;
}

#product-details > button:disabled {
  cursor: not-allowed;
  opacity: 0.65;
}

/* =========================
   FOOTER
   ========================= */

footer {
  margin-top: 3rem;
  padding: 1.5rem;
  border-top: 1px solid var(--border-color);
  background-color: var(--surface-color);
  text-align: center;
}

footer p {
  color: var(--secondary-color);
  font-size: 0.85rem;
}

/* =========================
   TABLET
   ========================= */

@media (max-width: 1024px) {
  header nav {
    gap: 1.25rem;
  }

  #product-details {
    column-gap: 2rem;
  }

  #product-details img {
    height: 380px;
  }
}

/* =========================
   MOBILE
   ========================= */

@media (max-width: 768px) {
  header nav {
    flex-wrap: wrap;
    gap: 0;
  }

  header nav > a {
    order: 1;
    flex: 1;
  }

  #header-actions {
    order: 2;
    gap: 0.5rem;
  }

  #cart-link {
    display: flex;
    align-items: center;
    min-height: 42px;
    padding: 0.5rem 0.7rem;
  }

  #menu-toggle {
    display: block;
  }

  #mobile-menu {
    order: 3;
    display: none;
    flex-basis: 100%;
    width: 100%;
    flex-direction: column;
    align-items: stretch;
    gap: 1rem;
    padding: 1rem 0 0;
  }

  #mobile-menu.menu-open {
    display: flex;
  }

  #product-search {
    order: initial;
    width: 100%;
    display: flex;
    flex-direction: column;
    align-items: stretch;
    gap: 0.5rem;
  }

  #product-search input {
    max-width: none;
  }

  #product-search button {
    width: 100%;
  }

  #auth-navigation {
    order: initial;
    display: flex;
    flex-direction: column;
    align-items: stretch;
    gap: 0;
    padding-top: 0.5rem;
    border-top: 1px solid var(--border-color);
  }

  #auth-navigation a,
  #auth-navigation button {
    width: 100%;
    padding: 0.85rem 0.5rem;
    text-align: left;
  }

  #auth-navigation a:hover,
  #auth-navigation button:hover {
    background-color: #f3f4f6;
    color: var(--text-color);
  }

  main {
    padding: 2rem 1rem;
  }

  main section h1 {
    font-size: 1.7rem;
  }

  #product-details {
    grid-template-columns: 1fr;
    padding: 1.25rem;
    column-gap: 0;
  }

  #product-details h2,
  #product-details img,
  #product-details > p:nth-of-type(1),
  #product-details > p:nth-of-type(2),
  #product-details > p:nth-of-type(3),
  #product-details label,
  #product-quantity,
  #product-details > button {
    grid-column: 1;
  }

  #product-details img {
    grid-row: 1;
    height: 300px;
    margin-bottom: 0.5rem;
  }

  #product-details h2 {
    grid-row: 2;
    margin-bottom: 0.25rem;
  }

  #product-details > p:nth-of-type(1) {
    grid-row: 3;
  }

  #product-details > p:nth-of-type(2) {
    grid-row: 4;
  }

  #product-details > p:nth-of-type(3) {
    grid-row: 5;
  }

  #product-details label {
    grid-row: 6;
  }

  #product-quantity {
    grid-row: 7;
  }

  #product-details > button {
    grid-row: 8;
  }
}