:root {
  --main-font: "Open Sans", sans-serif;

  /* Light mode */
  --primary-color: #0082c6;
  --text-color: #333;
  --navbar-link-color: white;
  --navbar-hover-bg: white;
  --navbar-hover-text: var(--primary-color);
  --dropdown-bg: #fff;
  --dropdown-text: #333;
  --dropdown-hover-bg: var(--primary-color);
  --dropdown-hover-text: white;
  --header-text-color: white;
  --header-overlay: rgba(0, 0, 0, 0.2);
}

/* Dark mode overrides */
@media (prefers-color-scheme: dark) {
  :root {
    --primary-color: #0082c6;
    --text-color: #e0e0e0;
    --navbar-link-color: white;
    --navbar-hover-bg: #fff;
    --navbar-hover-text: var(--primary-color);
    --dropdown-bg: #0082c6;
    --dropdown-text: #ddd;
    --dropdown-hover-bg: #fff;
    --dropdown-hover-text: #222;
    --header-text-color: #f0f0f0;
    --header-overlay: rgba(0, 0, 0, 0.5);
  }
}

/* ========================
   Navbar Styles (Desktop)
======================== */
.navbar {
  display: flex;
  position: fixed;
  top: 0;
  left: 0;
  z-index: 999;
  width: 100%;
  min-height: 72px;
  flex-wrap: wrap;
  background-color: var(--primary-color);
  align-items: center;
  justify-content: center;
}


.navbar > div {
  position: relative;
}

.navbar a {
  color: var(--navbar-link-color);
  padding: 25px 16px;
  text-decoration: none;
  font-weight: 450;
  display: block;
  transition: background-color 0.3s ease, color 0.3s ease;
}

.navbar > div > a:hover {
  background-color: var(--navbar-hover-bg);
  color: var(--navbar-hover-text);
}

/* Dropdown content */
.dropdown {
  display: none;
  position: absolute;
  top: 100%;
  left: 0;
  background-color: var(--dropdown-bg);
  min-width: 220px;
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.15);
  z-index: 999;
  overflow: hidden;
}

.dropdown a {
  padding: 20px 15px;
  color: var(--dropdown-text);
  text-align: left;
  white-space: nowrap;
  font-weight: 500;
  transition: background-color 0.3s, color 0.3s;
}

.dropdown a:hover {
  background-color: var(--dropdown-hover-bg);
  color: var(--dropdown-hover-text);
}

/* Show dropdown on hover (desktop) */
.navbar > div:hover .dropdown {
  display: block;
}

/* ========================
   Header with Background Image
======================== */
.logo {
  position: relative;
  height: 86px;
}

#header-content {
  position: relative;
  width: 100%;
  overflow: hidden;
  display: flex;
  justify-content: center;
  align-items: center;
  flex-direction: column;
  color: var(--header-text-color);
  text-align: center;
  font-family: var(--main-font);
  z-index: 1;

  /* CHÚ Ý: Tổng chiều cao = padding-top (navbar) + 300px */
  height: calc(300px + var(--navbar-height, 72px));
  padding-top: var(--navbar-height, 72px);
}


.bg-slide {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background-size: cover;
  background-position: center;
  opacity: 0;
  z-index: -1;
  animation: fadeinout 15s infinite;
}

.slide1 {
  background-image: url("../images/header_picture_1.jpg");
  animation-delay: 0s;
}

.slide2 {
  background-image: url("../images/header_picture_2.jpg");
  animation-delay: 5s;
}

.slide3 {
  background-image: url("../images/header_picture_3.jpg");
  animation-delay: 10s;
}

@keyframes fadeinout {
  0% {
    opacity: 0;
  }
  10% {
    opacity: 1;
  }
  35% {
    opacity: 1;
  }
  40% {
    opacity: 0;
  }
  100% {
    opacity: 0;
  }
}

#header-content::before {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background-color: var(--header-overlay);
  z-index: 0;
}

.header-title,
.header-time-place {
  position: relative;
  z-index: 1;
  text-align: center;
  padding: 0 1rem;
  text-shadow: 0 2px 6px rgba(0, 0, 0, 0.6);
}

.header-title {
  font-size: 2.5rem;
  font-weight: 550;
  margin-bottom: 0.5rem;
  color: var(--header-text-color);
}

.header-time-place {
  font-size: 1.25rem;
  font-weight: 500;
  opacity: 0.9;
  color: var(--header-text-color);
}

a {
  color: black;
  text-decoration: none;
  transition: color 0.3s ease;
}

a:hover {
  color: #0082c6; /* Màu xanh bạn chọn */
  text-decoration: none;
}

.section a {
  color: black;
  text-decoration: none;
  transition: color 0.3s ease;
}

.section a:hover {
  color: #0082c6;
  text-decoration: none;
}

/* ========================
   Mobile Responsive Styles
======================== */
@media screen and (min-width: 768px) {
  .nav-toggle {
    display: none;
  }

}
@media screen and (max-width: 768px) {
  .navbar {
    flex-direction: column;
    display: none;
    position: fixed;
    top: 0;
    left: 0;
    background-color: var(--primary-color);
    width: 100%;
    height: 100vh;
    z-index: 1000;
    justify-content: start;
  }

  .navbar.active {
    display: flex;
  }

  .navbar > div {
    width: 100%;
    text-align: left;
    position: relative;
  }

  .navbar a {
    width: 100%;
    font-size: 18px;
    padding-left: 40px;
  }

  .dropdown {
    padding-left: 20px;
    position: static;
    width: 100%;
    box-shadow: none;
  }

  .navbar-overlay {
    display: none;
  }

  .navbar-overlay.active {
    display: block;
    position: fixed;
    inset: 0;
    background: rgba(0, 0, 0, 0.5);
    z-index: 999;
  }

  /* Chỉ hiển thị nút nav-toggle trên mobile */
  .nav-toggle {
    display: block;
    position: fixed;
    top: 10px;
    right: 20px;
    font-size: 30px;
    background-color: #0082c6; /* màu nền */
    border: none;
    border-radius: 8px; /* bo góc */
    color: white;
    z-index: 1100;
    cursor: pointer;
    padding: 4px 10px; /* tuỳ chỉnh cho vừa vặn */
    box-shadow: 0 4px 8px rgba(0, 0, 0, 0.2); /* thêm bóng đổ nếu cần */
    transition: all 0.3s ease;
  }

  .dropdown {
    padding: 0;
    margin: 0;
  }

  #header-content {
    height: 450px;
  }

  .header-title {
    font-size: 1.5rem;
  }
}

@media screen and (min-width: 768px) and (max-width: 1200px) {
  .navbar {
    flex-direction: column;
    display: none;
    position: fixed;
    top: 0;
    left: 0;
    background-color: var(--primary-color);
    width: 100%;
    height: 100vh;
    z-index: 1000;
    justify-content: start;
  }

  .navbar.active {
    display: flex;
  }

  .navbar > div {
    width: 100%;
    text-align: left;
    position: relative;
  }

  .navbar a {
    width: 100%;
    font-size: 20px;
    padding-left: 48px;
  }

  .dropdown {
    padding-left: 24px;
    position: static;
    width: 100%;
    box-shadow: none;
    padding: 0;
    margin: 0;
  }

  .navbar-overlay {
    display: none;
  }

  .navbar-overlay.active {
    display: block;
    position: fixed;
    inset: 0;
    background: rgba(0, 0, 0, 0.5);
    z-index: 999;
  }

  /* Hiển thị nút nav-toggle ở tablet */
  .nav-toggle {
    display: block;
    position: fixed;
    top: 10px;
    right: 20px;
    font-size: 30px;
    background-color: #0082c6; /* màu nền */
    border: none;
    border-radius: 8px; /* bo góc */
    color: white;
    z-index: 1100;
    cursor: pointer;
    padding: 4px 10px; /* tuỳ chỉnh cho vừa vặn */
    box-shadow: 0 4px 8px rgba(0, 0, 0, 0.2); /* thêm bóng đổ nếu cần */
    transition: all 0.3s ease;
  }

}