/* ===== Reset ===== */
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

/* ===== Body ===== */
body {
  font-family: 'Roboto', Arial, sans-serif;
  background-color: #f3f4f6;
  color: #111827;
  line-height: 1.7;
}

/* ===== Header ===== */
header {
  background-color: #0f172a;
  color: #ffffff;
  padding: 20px;
  text-align: left;
  border-bottom: 1px solid #1f2937;
}

header h1 {
  font-size: 28px;
  font-weight: 700;
  color: #ffffff;
}

/* ===== Navigation ===== */
nav {
  position: sticky;
  top: 0;
  z-index: 999;
  display: flex;
  justify-content: center;
  flex-wrap: wrap;
  gap: 25px;
  background-color: #111827;
  padding: 12px 0;
  border-bottom: 2px solid #ff4fa3;
  box-shadow: 0 2px 6px rgba(0, 0, 0, 0.3);
}

nav a {
  color: #ffffff;
  text-decoration: none;
  font-weight: 600;
  font-size: 15px;
  transition: color 0.3s ease, transform 0.2s ease;
}

nav a:hover {
  color: #ff4fa3;
  transform: translateY(-2px);
}

/* ===== Main Content ===== */
main {
  max-width: 980px;
  margin: 50px auto;
  background: #ffffff;
  color: #111827;
  box-shadow: 0 4px 16px rgba(0, 0, 0, 0.1);
  border-radius: 12px;
  padding: 40px 60px;
  border-top: 4px solid #ff4fa3;
}

/* ===== Typography ===== */
main h1 {
  color: #ff4fa3;          /* hồng neon */
  text-align: center;      /* căn giữa tiêu đề */
  font-weight: 800;
  font-size: 28px;
  margin-bottom: 20px;
}

main h2, main h3 {
  color: #ff4fa3;
  margin-bottom: 16px;
  font-weight: 700;
  text-align: left;
}

main p {
  margin-bottom: 18px;
  color: #111827;
  font-size: 16px;
  text-align: justify;      /* căn đều cho đẹp đoạn văn */
}

a {
  color: #ff4fa3;
  text-decoration: none;
}

a:hover {
  color: #ff77b5;
  text-decoration: underline;
}

/* ===== Buttons ===== */
button {
  background: linear-gradient(90deg, #ff4fa3, #ff77b5);
  color: #ffffff;
  padding: 10px 22px;
  border: none;
  border-radius: 8px;
  font-weight: 700;
  cursor: pointer;
  font-size: 16px;
  transition: transform 0.2s ease, filter 0.2s ease;
}

button:hover {
  transform: translateY(-2px);
  filter: brightness(1.05);
}

/* ===== Footer ===== */
footer {
  background-color: #0f172a;
  color: #9ca3af;
  text-align: center;
  padding: 20px 0;
  margin-top: 40px;
  border-top: 2px solid #ff4fa3;
}

footer a {
  color: #ff4fa3;
  text-decoration: none;
}

footer a:hover {
  color: #ff77b5;
}

/* ===== Accent helper ===== */
.accent {
  color: #ff4fa3;
  font-weight: 600;
}


/* ===== Center Header Content ===== */
header {
  display: flex;
  justify-content: center;   /* căn giữa ngang */
  align-items: center;       /* căn giữa dọc nếu cao */
  flex-direction: column;    /* xếp nội dung dọc */
  text-align: center;        /* chữ trong header căn giữa */
  background-color: #0f172a; /* vẫn giữ màu xanh đen */
  color: #ffffff;
  padding: 25px 0;
  border-bottom: 1px solid #1f2937;
}

header h1 {
  color: #ffffff;
  font-size: 30px;
  font-weight: 800;
  text-align: center;
  margin: 0;
}