:root {
  --bg-gradient: linear-gradient(to bottom right, #ebf4ff, #c7d2fe);
  --card-bg: #ffffff;
  --text: #1f2937;
  --subtext: #4b5563;
  --border: #d1d5db;
  --error-bg: #fee2e2;
  --error-text: #b91c1c;
  --result-bg: linear-gradient(to right, #eef2ff, #e0e7ff);
}
body.dark {
  --bg-gradient: linear-gradient(to bottom right, #111827, #1f2937);
  --card-bg: #1f2937;
  --text: #f9fafb;
  --subtext: #9ca3af;
  --border: #374151;
  --error-bg: #7f1d1d;
  --error-text: #fecaca;
  --result-bg: linear-gradient(to right, #1f2937, #374151);
}
* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
  font-family: system-ui, sans-serif;
}
body {
  min-height: 100vh;
  background: var(--bg-gradient);
  display: flex;
  justify-content: center;
  align-items: start;
  padding: 2rem;
  color: var(--text);
  transition: background 0.3s ease, color 0.3s ease;
}
.container {
  max-width: 700px;
  width: 100%;
}
.header {
  text-align: center;
  margin-bottom: 2rem;
}
.top-bar {
  display: flex;
  justify-content: space-between;
  align-items: center;
}
.icon {
  font-size: 2.5rem;
}

.theme-toggle {
  border: none;
  background: transparent;
  font-size: 1.5rem;
  cursor: pointer;
}
.card {
  background: var(--card-bg);
  border-radius: 1rem;
  box-shadow: 0 4px 20px rgba(0,0,0,0.1);
  padding: 2rem;
  transition: background 0.3s ease;
}
.card h2 {
  font-size: 1.5rem;
  margin-bottom: 0.3rem;
}
.card .description {
  color: var(--subtext);
  margin-bottom: 1.5rem;
}
.form {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1rem;
}
.form-group {
  display: flex;
  flex-direction: column;
  gap: 0.3rem;
}
input, select {
  padding: 0.6rem;
  border: 1px solid var(--border);
  border-radius: 0.5rem;
  font-size: 1rem;
  background: var(--card-bg);
  color: var(--text);
  transition: background 0.3s ease, color 0.3s ease, border 0.3s ease;
}
button#convertBtn {
  margin-top: 1.5rem;
  width: 100%;
  padding: 0.8rem;
  font-size: 1.1rem;
  font-weight: bold;
  border: none;
  border-radius: 0.6rem;
  background: linear-gradient(to right, #2563eb, #4f46e5);
  color: white;
  cursor: pointer;
  transition: 0.2s ease;
}
button#convertBtn:hover {
  opacity: 0.9;
}
.error {
  margin-top: 1rem;
  padding: 0.8rem;
  border-radius: 0.5rem;
  background: var(--error-bg);
  color: var(--error-text);
  font-weight: 500;
}
.hidden {
  display: none;
}
.results {
  margin-top: 2rem;
  padding: 1.5rem;
  border-radius: 0.8rem;
  background: var(--result-bg);
  border: 1px solid var(--border);
  transition: background 0.3s ease, border 0.3s ease;
}
.results h3 {
  text-align: center;
  margin-bottom: 1rem;
}
.result-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(120px,1fr));
  gap: 1rem;
}
.result-box {
  text-align: center;
  background: var(--card-bg);
  padding: 1rem;
  border-radius: 0.5rem;
  box-shadow: 0 2px 8px rgba(0,0,0,0.05);
  transition: background 0.3s ease;
}
.value {
  font-size: 1.4rem;
  font-weight: bold;
  color: #2563eb;
}
.label {
  font-size: 0.9rem;
  color: var(--subtext);
}
.info {
  margin-top: 1rem;
  text-align: center;
  font-size: 0.9rem;
  color: var(--subtext);
}
.footer {
  margin-top: 2rem;
  text-align: center;
  font-size: 0.85rem;
  color: var(--subtext);
}