body.dark-mode {
  background: #181a1b;
  color: #e0e0e0;
}
body.dark-mode header, body.dark-mode footer {
  background: #23272b;
  color: #e0e0e0;
  border-bottom: 1px solid #444;
}
body.dark-mode .category {
  background: #222326;
  color: #e0e0e0;
  border: 1px solid #333;
  box-shadow: 0 2px 8px rgba(0,0,0,0.12);
}
body.dark-mode .converter {
  background: #181a1b;
  color: #e0e0e0;
  border: 1px solid #333;
  box-shadow: 0 1px 4px rgba(0,0,0,0.10);
}
body.dark-mode label {
  color: #b0b0b0;
}
body.dark-mode input[type="number"] {
  background: #23272b;
  color: #e0e0e0;
  border: 1px solid #555;
}
body.dark-mode input[type="number"]:invalid {
  background: #2c1a1a;
  border-color: #dc3545;
}
body.dark-mode button {
  background: #3a6ea5;
  color: #fff;
  border: 1px solid #2c4a6b;
  box-shadow: 0 1px 2px rgba(0,0,0,0.10);
}
body.dark-mode button:hover {
  background: #26547c;
  color: #fff;
}
body.dark-mode .result {
  background: #23272b;
  color: #a3e635;
  border: 1px solid #333;
}
body {
  font-family: 'Inter', 'Segoe UI', Arial, sans-serif;
  padding: 2.5rem 0 2rem 0;
  background: #f6f7f9;
  margin: 0;
}
header, footer {
  text-align: center;
  padding: 1.2rem 0 1rem 0;
  background: #f3f4f6;
  color: #222;
  margin-bottom: 2rem;
  border-bottom: 1px solid #e0e0e0;
  letter-spacing: 0.5px;
}
h1 {
  font-size: 2.2rem;
  margin-bottom: 0.3rem;
  font-weight: 700;
  letter-spacing: 0.5px;
}
.categories {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(340px, 1fr));
  gap: 2.2rem;
  margin: 0 1.5rem;
}
.category {
  background: #f9fafb;
  border-radius: 12px;
  padding: 1.2rem 1rem 1rem 1rem;
  margin-bottom: 2rem;
  box-shadow: 0 2px 8px rgba(60,60,60,0.04);
  border: 1px solid #e0e0e0;
}
.category h2 {
  margin-top: 0;
  color: #2d3748;
  font-size: 1.25rem;
  font-weight: 600;
  letter-spacing: 0.2px;
}
.converter {
  background: #fff;
  padding: 1rem;
  margin-bottom: 1rem;
  border-radius: 8px;
  box-shadow: 0 1px 4px rgba(60,60,60,0.03);
  border: 1px solid #e0e0e0;
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
}
label {
  font-weight: 500;
  margin-bottom: 0.2rem;
  color: #2d3748;
  letter-spacing: 0.1px;
}
input[type="number"] {
  padding: 0.5rem;
  border: 1px solid #bfc8d0;
  border-radius: 4px;
  font-size: 1rem;
  transition: border-color 0.2s;
  background: #f7fafc;
  color: #222;
}
input[type="number"]:invalid {
  border-color: #dc3545;
  background: #fff0f0;
}
button {
  background: linear-gradient(90deg, #3a6ea5 0%, #26547c 100%);
  color: #fff;
  border: 1px solid #2c4a6b;
  border-radius: 4px;
  padding: 0.5rem 1rem;
  font-size: 1rem;
  cursor: pointer;
  transition: background 0.2s, box-shadow 0.2s;
  box-shadow: 0 1px 2px rgba(60,60,60,0.07);
  font-weight: 500;
  letter-spacing: 0.2px;
}
button:hover {
  background: linear-gradient(90deg, #26547c 0%, #3a6ea5 100%);
}
.result {
  font-weight: 600;
  margin-top: 0.5rem;
  background: #e6f4ea;
  color: #26547c;
  padding: 0.5rem;
  border-radius: 4px;
  font-size: 1.08rem;
  min-height: 2rem;
  transition: background 0.2s;
  border: 1px solid #bfc8d0;
  letter-spacing: 0.1px;
}
@media (max-width: 600px) {
  .categories {
    grid-template-columns: 1fr;
    margin: 0;
  }
}