* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  transition: all 0.6s;
}

body {
  background-color: #121212;
  color: #eee;
  font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
  min-height: 90vh;
  display: flex;
  flex-direction: column;
}

.navbar {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  background: rgba(18, 18, 18, 0.75);
  backdrop-filter: blur(8px);
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 0.7rem 2rem;
  z-index: 1000;
  border-bottom: 1px solid #333;
  color: #fff;
}

.navbar .logo {
  font-weight: 700;
  font-size: 1.5rem;
  user-select: none;
}

.navbar ul {
  list-style: none;
  display: flex;
  gap: 1.8rem;
}

.navbar ul li a {
  text-decoration: none;
  color: #ddd;
  font-weight: 600;
  transition: color 0.3s ease;
  user-select: none;
}

#active {
  color: #43a4ff;
}

.navbar ul li a:hover,
.navbar ul li a:focus {
  color: #4f94d4;
  outline: none;
}

.footer {
  position: fixed;
  bottom: 0;
  left: 0;
  width: 100%;
  background: rgba(18, 18, 18, 0.75);
  text-align: center;
  padding: 1rem 2rem;
  color: #bbb;
  font-size: 0.9rem;
  user-select: none;
}

main {
  flex-grow: 1;
  max-width: 900px;
  margin: 5rem auto 4rem auto;
  padding: 2rem 3rem;
  color: #eee;
}

.hero {
  text-align: center;
  margin-bottom: 3rem;
}

.hero h1 {
  font-size: 2.8rem;
  margin-bottom: 0.6rem;
  user-select: none;
}

.hero p {
  font-size: 1.25rem;
  color: #bbb;
}

.tool {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 1rem;
  margin-bottom: 3rem;
}

.tool input[type="number"] {
  padding: 0.8rem 1.2rem;
  font-size: 1.1rem;
  border-radius: 8px;
  border: none;
  width: 100%;
  max-width: 400px;
  background-color: #222;
  color: #eee;
  transition: background-color 0.3s ease, border-color 0.3s ease;
}

.tool input[type="number"]:focus {
  outline: none;
  background-color: #2a2a2a;
  border: 2px solid #4f94d4;
}

.tool button {
  background-color: #4f94d4;
  color: white;
  border: none;
  padding: 0.85rem 2.2rem;
  font-size: 1.1rem;
  font-weight: 700;
  border-radius: 8px;
  cursor: pointer;
  transition: background-color 0.3s ease;
}

.tool button:hover,
.tool button:focus {
  background-color: #3a78c2;
  outline: none;
}

.result {
  font-size: 1.2rem;
  text-align: center;
  margin-top: 1rem;
}

@media (max-width: 600px) {
  main {
    margin: 6rem 1.5rem 5rem 1.5rem;
    padding: 1.5rem;
  }

  .navbar ul {
    gap: 1rem;
  }

  .hero h1 {
    font-size: 2rem;
  }

  .tool input[type="number"] {
    max-width: 100%;
  }

  .result {
    font-size: 1rem;
  }
}