/* Reset nhẹ */
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
}

body {
  background: #f3f4f6;
  color: #111827;
  line-height: 1.6;
}

a {
  text-decoration: none;
  color: inherit;
}

/* Header */
header {
  background: linear-gradient(135deg, #111827, #1f2937);
  color: #f9fafb;
  padding: 16px 24px;
  position: sticky;
  top: 0;
  z-index: 10;
}

.nav-container {
  max-width: 1100px;
  margin: auto;
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.logo {
  font-size: 1.3rem;
  font-weight: 700;
}

/* Layout */
main {
  max-width: 1100px;
  margin: 20px auto 40px;
  padding: 0 16px;
  display: grid;
  grid-template-columns: 2fr 1fr;
  gap: 24px;
}

/* Hero */
.hero {
  grid-column: 1 / -1;
  background: #111827;
  color: #f9fafb;
  border-radius: 18px;
  padding: 24px 20px;
}

.hero-title {
  font-size: 1.8rem;
  font-weight: 700;
  margin-bottom: 6px;
}

.hero-subtitle {
  font-size: 0.95rem;
  color: #e5e7eb;
}

.highlight {
  font-weight: 600;
  color: #facc15;
}

/* Card */
.card {
  background: #ffffff;
  border-radius: 16px;
  padding: 18px 16px;
  box-shadow: 0 8px 20px rgba(15, 23, 42, 0.07);
  border: 1px solid #e5e7eb;
  margin-bottom: 20px;
}

.card h2 {
  font-size: 1.15rem;
  margin-bottom: 8px;
}

.card p {
  font-size: 0.9rem;
  color: #4b5563;
}

.card ul {
  margin-left: 18px;
  margin-top: 6px;
  font-size: 0.9rem;
  color: #4b5563;
}

.card ul li + li {
  margin-top: 4px;
}

/* Ô nhập km */
.km-input-box {
  margin-top: 12px;
  padding: 14px;
  background: #f9fafb;
  border-radius: 12px;
  border: 1px solid #e5e7eb;
}

.km-input-box label {
  font-size: 0.9rem;
  font-weight: 500;
}

.km-input-box input {
  width: 100%;
  padding: 10px;
  font-size: 1rem;
  border-radius: 8px;
  border: 1px solid #d1d5db;
  margin-top: 8px;
}

/* Nút bấm */
.btn-check {
  margin-top: 10px;
  padding: 10px 16px;
  border-radius: 999px;
  border: none;
  cursor: pointer;
  font-size: 0.95rem;
  font-weight: 600;
  background: #facc15;
  color: #111827;
  transition: transform 0.15s, box-shadow 0.15s;
}

.btn-check:hover {
  transform: translateY(-1px);
  box-shadow: 0 8px 18px rgba(15, 23, 42, 0.18);
}

/* Kết quả */
.km-result {
  margin-top: 12px;
  background: #fff8e1;
  padding: 14px;
  border-radius: 10px;
  border: 1px solid #facc15;
  font-size: 0.9rem;
  display: none;
}

.km-result h3 {
  font-size: 0.95rem;
  margin-bottom: 6px;
}

.km-result ul {
  margin-left: 18px;
}

/* Sidebar */
aside {
  font-size: 0.9rem;
}

/* Responsive */
@media (max-width: 900px) {
  main {
    grid-template-columns: 1fr;
  }
}