:root {
  --bg: #0f172a;
  --bg-gradient-start: #0f172a;
  --bg-gradient-end: #1e1b4b;
  --card: #1e293b;
  --field: #0f172a;
  --border: #334155;
  --text: #f1f5f9;
  --sub: #94a3b8;
  --accent: #fbbf24;
  --accent-text: #1e1b4b;
  --shadow: rgba(0, 0, 0, 0.4);
}

:root[data-theme="light"] {
  --bg: #f8fafc;
  --bg-gradient-start: #e0e7ff;
  --bg-gradient-end: #f8fafc;
  --card: #ffffff;
  --field: #f1f5f9;
  --border: #cbd5e1;
  --text: #1e293b;
  --sub: #64748b;
  --accent: #f59e0b;
  --accent-text: #1e1b4b;
  --shadow: rgba(15, 23, 42, 0.12);
}

:root[data-theme="green"] {
  --bg: #eaf3e6;
  --bg-gradient-start: #dcebd6;
  --bg-gradient-end: #eef6ea;
  --card: #f4f9f1;
  --field: #e3f0dd;
  --border: #b7d6ac;
  --text: #26401f;
  --sub: #5f7a55;
  --accent: #6f9e5c;
  --accent-text: #f4f9f1;
  --shadow: rgba(38, 64, 31, 0.15);
}

:root[data-theme="blue"] {
  --bg: #eaf2fb;
  --bg-gradient-start: #dbe9fa;
  --bg-gradient-end: #f0f7ff;
  --card: #ffffff;
  --field: #e6f0fc;
  --border: #b6d4f2;
  --text: #17324d;
  --sub: #4d7ba8;
  --accent: #2f80ed;
  --accent-text: #ffffff;
  --shadow: rgba(23, 50, 77, 0.15);
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  background: linear-gradient(135deg, var(--bg-gradient-start), var(--bg-gradient-end));
  font-family: "Apple SD Gothic Neo", "Malgun Gothic", sans-serif;
  color: var(--text);
  padding: 20px;
  transition: background 0.2s ease, color 0.2s ease;
}

.app {
  position: relative;
  width: 100%;
  max-width: 480px;
  background: var(--card);
  border-radius: 20px;
  padding: 32px 24px;
  box-shadow: 0 20px 50px var(--shadow);
  transition: background 0.2s ease;
}

.nav-link {
  position: absolute;
  top: 16px;
  left: 16px;
  font-size: 0.75rem;
  color: var(--sub);
  text-decoration: none;
  border: 1px solid var(--border);
  border-radius: 20px;
  padding: 8px 12px;
  background: var(--field);
}

.nav-link:hover {
  opacity: 0.85;
}

.theme-toggle {
  position: absolute;
  top: 16px;
  right: 16px;
  width: 36px;
  height: 36px;
  border: 1px solid var(--border);
  border-radius: 50%;
  background: var(--field);
  color: var(--text);
  font-size: 1rem;
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  padding: 0;
}

.theme-toggle:hover {
  opacity: 0.85;
}

h1 {
  text-align: center;
  font-size: 1.5rem;
  margin: 0 0 4px;
}

.desc {
  text-align: center;
  color: var(--sub);
  font-size: 0.85rem;
  margin-bottom: 24px;
  line-height: 1.5;
}

label {
  display: block;
  font-size: 0.82rem;
  color: var(--sub);
  margin-bottom: 6px;
}

.field {
  margin-bottom: 16px;
}

input[type="text"],
input[type="email"],
textarea,
button {
  width: 100%;
  padding: 10px;
  border-radius: 10px;
  border: 1px solid var(--border);
  font-size: 0.95rem;
  background: var(--field);
  color: var(--text);
  font-family: inherit;
}

textarea {
  resize: vertical;
}

#submitBtn {
  display: block;
  width: 100%;
  padding: 14px;
  background: var(--accent);
  color: var(--accent-text);
  font-weight: 700;
  font-size: 1rem;
  cursor: pointer;
  border-radius: 12px;
  border: none;
  margin-top: 8px;
  transition: transform 0.1s ease, opacity 0.2s ease;
}

#submitBtn:hover {
  opacity: 0.9;
}

#submitBtn:active {
  transform: scale(0.98);
}

#submitBtn:disabled {
  opacity: 0.6;
  cursor: not-allowed;
}

.notice {
  font-size: 0.78rem;
  color: var(--sub);
  background: var(--field);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 10px 12px;
  margin-top: 12px;
  line-height: 1.5;
}

.notice.error {
  color: #f87171;
  border-color: #f87171;
}

.notice.success {
  color: #34d399;
  border-color: #34d399;
}

.footer-note {
  margin-top: 20px;
  text-align: center;
  color: var(--sub);
  font-size: 0.75rem;
  line-height: 1.5;
}

.site-nav {
  margin-top: 16px;
  text-align: center;
  font-size: 0.72rem;
}

.site-nav a {
  color: var(--sub);
  text-decoration: none;
  margin: 0 6px;
}

.site-nav a:hover {
  text-decoration: underline;
}