h1, h2, h3, h4 {
    font-size: 24px;
    text-shadow: 1px 1px 0 #000; /* Viền chữ màu đen */
}

img {
    display: block;
    margin-left: auto;
    margin-right: auto;
}

div:first-of-type {
    background-color: #F3FDE8;
    padding: 20px;
}

div:last-of-type {
    background-image: url('img/background.jpg');
    background-repeat: repeat;
    text-align: center;
    padding: 20px;
}

table {
    width: 100%;
    border-collapse: collapse;
    margin-top: 20px;
}

th, td {
    border: 1px solid black;
    padding: 10px;
    text-align: center;
}

nav, footer {
    background-color: #d4f2f4;
    color: #0b0848;
    padding: 10px;
    text-align: center;
}

nav a {
    margin: 0 15px;
    text-decoration: none;
    color: #0b0848;
    font-weight: bold;
}

footer p {
    margin: 0;
}

/* === Hiệu ứng ảnh === */
#avatar {
  display: block;
  border-radius: 10px; /* mặc định */
  box-shadow: 0 0 25px rgba(202, 237, 255, 0.5),
              0 0 45px rgba(216, 180, 248, 0.3);
  transition: transform 0.3s ease, border 0.3s ease, box-shadow 0.4s ease;
  cursor: pointer;
  object-fit: cover;
  background: radial-gradient(circle at center, #fefefe, #e1f5fe);
}

#avatar:hover {
  /* JS vẫn sẽ scale + border riêng, nên ở đây chỉ thêm ánh sáng */
  box-shadow: 0 0 35px rgba(202, 237, 255, 0.8),
              0 0 60px rgba(216, 180, 248, 0.6);
  filter: brightness(1.05);
}

/* === Nút Lên đầu trang === */
#backToTop {
  display: none;
  position: fixed;
  bottom: 20px;
  right: 20px;
  background-color: #CAEDFF;
  color: black;
  border: none;
  border-radius: 50%;
  width: 40px;
  height: 40px;
  cursor: pointer;
  font-size: 20px;
}

#backToTop:hover {
  background-color: #CAEDFF;
}