@import url('https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600;700;800&display=swap');

* { box-sizing: border-box; margin: 0; padding: 0; }

:root {
  --bg-primary: #f5f6fa;
  --bg-secondary: #fff;
  --text-primary: #1a1a2e;
  --text-secondary: #555;
  --text-light: #999;
  --border-color: #e2e5ef;
  --shadow: rgba(0,0,0,0.06);
  --primary-color: #4f7df3;
  --primary-light: rgba(79,125,243,0.08);
  --primary-glow: rgba(79,125,243,0.2);
  --gradient-primary: linear-gradient(135deg, #4f7df3, #7c5cf5);
  --danger-color: #ef4444;
  --success-color: #10b981;
  --transition: cubic-bezier(0.4, 0, 0.2, 1);
}

html.dark-mode,
body.dark-mode {
  --bg-primary: #0c0c18;
  --bg-secondary: #161627;
  --text-primary: #eaeaf2;
  --text-secondary: #a0a0b8;
  --text-light: #8686ab;
  --border-color: #252540;
  --shadow: rgba(0,0,0,0.35);
  --primary-light: rgba(79,125,243,0.12);
  --primary-glow: rgba(79,125,243,0.3);
}

body {
  font-family: 'Inter', 'Segoe UI', -apple-system, sans-serif;
  background: var(--bg-primary);
  color: var(--text-primary);
  min-height: 100vh;
  transition: background 0.4s var(--transition), color 0.4s var(--transition);
}

body::before {
  content: '';
  position: fixed;
  top: -200px;
  right: -200px;
  width: 500px;
  height: 500px;
  background: radial-gradient(circle, rgba(79,125,243,0.07) 0%, transparent 65%);
  pointer-events: none;
}

.container {
  max-width: 420px;
  margin: 0 auto;
  padding: 36px 24px 60px;
  position: relative;
  z-index: 1;
}

/* ── Header ── */
header {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  margin-bottom: 32px;
  gap: 20px;
}

.header-left { flex: 1; }

.home-link {
  display: inline-flex;
  align-items: center;
  gap: 4px;
  font-size: 0.82rem;
  color: var(--primary-color);
  text-decoration: none;
  margin-bottom: 10px;
  font-weight: 600;
  padding: 4px 12px 4px 8px;
  border-radius: 20px;
  background: var(--primary-light);
  transition: all 0.25s var(--transition);
}

.home-link:hover {
  background: var(--primary-glow);
  transform: translateX(-3px);
}

.header-left h1 {
  font-size: 2rem;
  font-weight: 800;
  letter-spacing: -1px;
  margin-bottom: 6px;
  background: var(--gradient-primary);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

.subtitle {
  font-size: 0.88rem;
  color: var(--text-secondary);
  font-weight: 400;
}

.header-right {
  display: flex;
  align-items: center;
  gap: 10px;
}

header button {
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  cursor: pointer;
  font-size: 1.05rem;
  padding: 9px 12px;
  border-radius: 12px;
  transition: all 0.25s var(--transition);
  color: var(--text-primary);
  line-height: 1;
}

header button:hover {
  background: var(--primary-light);
  border-color: var(--primary-color);
  transform: translateY(-2px);
  box-shadow: 0 4px 12px var(--shadow);
}

/* 다크모드/도움말/언어 아이콘 버튼 — 홈페이지와 동일한 구조 */
.icon-btn {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 38px;
  height: 38px;
  padding: 0;
  border: 1.5px solid var(--border-color);
  border-radius: 10px;
  background: var(--bg-primary);
  cursor: pointer;
  transition: all 0.25s var(--transition);
  color: var(--text-secondary);
}

.icon-btn:hover {
  border-color: var(--primary-color);
  background: var(--primary-light);
  color: var(--primary-color);
  transform: none;
  box-shadow: none;
}

.theme-icon {
  width: 18px;
  height: 18px;
}

.lang-select {
  position: relative;
}

.lang-toggle {
  position: absolute;
  top: calc(100% + 8px);
  right: 0;
  min-width: 160px;
  padding: 6px;
  border: 1.5px solid var(--border-color);
  border-radius: 12px;
  background: var(--bg-secondary);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  box-shadow: 0 8px 24px var(--shadow);
  opacity: 0;
  visibility: hidden;
  transform: translateY(-6px);
  transition: all 0.2s var(--transition);
  z-index: 200;
}

.lang-select.open .lang-toggle {
  opacity: 1;
  visibility: visible;
  transform: translateY(0);
}

.lang-option {
  display: flex;
  align-items: center;
  justify-content: space-between;
  width: 100%;
  border: none;
  background: none;
  cursor: pointer;
  font-family: inherit;
  font-size: 0.86rem;
  font-weight: 600;
  color: var(--text-secondary);
  padding: 9px 10px;
  border-radius: 8px;
  transition: all 0.2s var(--transition);
}

.lang-option:hover {
  background: var(--primary-light);
  color: var(--primary-color);
}

.lang-option.active {
  color: var(--primary-color);
}

.lang-option .lang-check {
  opacity: 0;
  color: var(--primary-color);
}

.lang-option.active .lang-check {
  opacity: 1;
}

/* ── Calculator ── */
.calc-wrap {
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: 20px;
  overflow: hidden;
  box-shadow: 0 4px 24px var(--shadow);
}

.calc-display {
  padding: 28px 24px 20px;
  text-align: right;
  min-height: 100px;
  display: flex;
  flex-direction: column;
  justify-content: flex-end;
}

.calc-expression {
  font-size: 0.9rem;
  color: var(--text-light);
  font-weight: 500;
  min-height: 1.4em;
  word-break: break-all;
  margin-bottom: 8px;
}

.calc-result {
  font-size: 2.8rem;
  font-weight: 800;
  color: var(--text-primary);
  line-height: 1.1;
  font-variant-numeric: tabular-nums;
  word-break: break-all;
  transition: color 0.2s;
}

/* ── Memory indicator ── */
.calc-display-top {
  display: flex;
  justify-content: flex-start;
  min-height: 18px;
}

.calc-mem-indicator {
  font-size: 0.7rem;
  font-weight: 800;
  color: var(--primary-color);
  background: var(--primary-light);
  padding: 2px 8px;
  border-radius: 6px;
  letter-spacing: 0.5px;
}

/* ── Memory buttons ── */
.calc-memory {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 1px;
  background: var(--border-color);
  border-top: 1px solid var(--border-color);
}

.calc-btn.mem {
  font-size: 0.9rem;
  font-weight: 700;
  padding: 12px;
  color: var(--text-secondary);
  background: var(--bg-primary);
}

.calc-btn.mem:hover {
  background: var(--primary-light);
  color: var(--primary-color);
}

/* ── Buttons ── */
.calc-buttons {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 1px;
  background: var(--border-color);
  border-top: 1px solid var(--border-color);
}

.calc-btn {
  border: none;
  outline: none;
  cursor: pointer;
  font-family: inherit;
  font-size: 1.25rem;
  font-weight: 600;
  padding: 22px;
  transition: all 0.15s var(--transition);
  background: var(--bg-secondary);
  color: var(--text-primary);
}

.calc-btn:hover {
  background: var(--primary-light);
}

.calc-btn:active {
  background: var(--primary-glow);
  transform: scale(0.95);
}

.calc-btn.fn {
  color: var(--primary-color);
  font-weight: 700;
}

.calc-btn.op {
  background: var(--primary-light);
  color: var(--primary-color);
  font-size: 1.4rem;
  font-weight: 700;
}

.calc-btn.op:hover {
  background: var(--primary-glow);
}

.calc-btn.op.active {
  background: var(--primary-color);
  color: #fff;
}

.calc-btn.eq {
  background: var(--primary-color);
  color: #fff;
  font-size: 1.4rem;
  font-weight: 700;
}

.calc-btn.eq:hover {
  filter: brightness(1.1);
}

.calc-btn.zero {
  grid-column: span 2;
  text-align: left;
  padding-left: 32px;
}

/* ── History ── */
.history-section {
  margin-top: 24px;
  background: var(--bg-secondary);
  border: 1px solid var(--border-color);
  border-radius: 16px;
  padding: 20px;
}

.history-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 14px;
}

.history-header h2 {
  font-size: 0.95rem;
  font-weight: 700;
  color: var(--text-primary);
}

.action-btn {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 6px 14px;
  border: 1.5px solid var(--border-color);
  border-radius: 10px;
  background: var(--bg-secondary);
  color: var(--text-secondary);
  font-size: 0.78rem;
  font-weight: 600;
  font-family: inherit;
  cursor: pointer;
  transition: all 0.25s var(--transition);
}

.action-btn:hover {
  border-color: var(--primary-color);
  color: var(--primary-color);
  background: var(--primary-light);
}

.history-list {
  list-style: none;
  max-height: 240px;
  overflow-y: auto;
}

.history-list li {
  padding: 10px 0;
  border-bottom: 1px solid var(--border-color);
  font-size: 0.85rem;
  color: var(--text-secondary);
  display: flex;
  justify-content: space-between;
  cursor: pointer;
  transition: color 0.2s;
}

.history-list li:last-child {
  border-bottom: none;
}

.history-list li:hover {
  color: var(--primary-color);
}

.history-list .hist-expr {
  font-weight: 500;
}

.history-list .hist-result {
  font-weight: 700;
  color: var(--text-primary);
}

.hist-main {
  display: flex;
  flex-direction: column;
  gap: 2px;
  flex: 1;
  min-width: 0;
}

.hist-copy-btn {
  flex-shrink: 0;
  border: none;
  background: none;
  color: var(--text-light);
  font-size: 1rem;
  cursor: pointer;
  padding: 2px 6px;
  border-radius: 6px;
  transition: all 0.2s;
  opacity: 0;
}

.history-list li:hover .hist-copy-btn {
  opacity: 1;
  color: var(--primary-color);
}

.hist-copy-btn:hover {
  background: var(--primary-light);
}

/* ── Limit flash ── */
@keyframes limitFlash {
  0%   { color: var(--text-primary); }
  25%  { color: var(--danger-color); }
  75%  { color: var(--danger-color); }
  100% { color: var(--text-primary); }
}

.calc-result.limit-flash {
  animation: limitFlash 0.4s ease;
}

/* ── Modal ── */
.modal {
  position: fixed;
  inset: 0;
  background: rgba(0,0,0,0.45);
  backdrop-filter: blur(6px);
  -webkit-backdrop-filter: blur(6px);
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 100;
  animation: fadeBg 0.2s ease;
  padding: 20px;
}

@keyframes fadeBg {
  from { opacity: 0; }
  to   { opacity: 1; }
}

.modal-box {
  background: var(--bg-secondary);
  color: var(--text-primary);
  border-radius: 20px;
  padding: 28px;
  width: 100%;
  max-width: 400px;
  box-shadow: 0 20px 60px rgba(0,0,0,0.2);
  animation: modalIn 0.35s var(--transition);
  border: 1px solid var(--border-color);
  position: relative;
  overflow: hidden;
}

.modal-box::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 4px;
  background: var(--gradient-primary);
}

@keyframes modalIn {
  from { transform: translateY(24px) scale(0.95); opacity: 0; }
  to   { transform: translateY(0) scale(1); opacity: 1; }
}

.modal-box h2 {
  margin-bottom: 18px;
  font-size: 1.3rem;
  font-weight: 700;
  letter-spacing: -0.5px;
}

.shortcuts {
  display: flex;
  flex-direction: column;
  gap: 10px;
  margin-bottom: 20px;
}

.shortcut-item {
  display: flex;
  align-items: center;
  gap: 10px;
  font-size: 0.88rem;
  padding: 8px 12px;
  background: var(--bg-primary);
  border-radius: 10px;
  transition: background 0.2s;
}

.shortcut-item:hover {
  background: var(--primary-light);
}

.shortcut-item kbd {
  background: var(--gradient-primary);
  color: #fff;
  padding: 4px 10px;
  border-radius: 6px;
  font-size: 0.72rem;
  font-weight: 700;
  font-family: 'Inter', monospace;
  box-shadow: 0 2px 6px var(--primary-glow);
  letter-spacing: 0.3px;
}

.shortcut-item span {
  color: var(--text-secondary);
  font-weight: 500;
}

.modal-close-btn {
  width: 100%;
  background: var(--gradient-primary);
  color: #fff;
  border: none;
  border-radius: 12px;
  padding: 12px;
  font-size: 0.92rem;
  font-weight: 600;
  font-family: inherit;
  cursor: pointer;
  transition: all 0.25s;
  box-shadow: 0 3px 10px var(--primary-glow);
}

.modal-close-btn:hover {
  transform: translateY(-2px);
  box-shadow: 0 6px 18px var(--primary-glow);
}

/* ── Toast ── */
.toast {
  position: fixed;
  bottom: 32px;
  left: 50%;
  transform: translateX(-50%) translateY(0);
  background: var(--bg-secondary);
  color: var(--text-primary);
  padding: 12px 24px;
  border-radius: 12px;
  font-size: 0.85rem;
  font-weight: 600;
  z-index: 200;
  box-shadow: 0 8px 30px rgba(0,0,0,0.15);
  border: 1px solid var(--border-color);
  animation: toastIn 0.35s var(--transition);
}

@keyframes toastIn {
  from { transform: translateX(-50%) translateY(16px); opacity: 0; }
  to   { transform: translateX(-50%) translateY(0); opacity: 1; }
}

/* ── Scrollbar ── */
::-webkit-scrollbar { width: 6px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: var(--border-color); border-radius: 6px; }

::selection {
  background: var(--primary-glow);
  color: var(--text-primary);
}

*:focus-visible {
  outline: 2px solid var(--primary-color);
  outline-offset: 2px;
}

/* ── Responsive ── */
@media (max-width: 600px) {
  .container { padding: 24px 16px 50px; }
  .header-left h1 { font-size: 1.5rem; }
  .lang-toggle { min-width: 140px; right: -4px; }
  .lang-option { padding: 8px 8px; font-size: 0.8rem; }
  .calc-result { font-size: 2.2rem; }
  .calc-btn { padding: 18px; font-size: 1.1rem; }
  .calc-btn.op, .calc-btn.eq { font-size: 1.25rem; }
}

/* 모바일 가로 스크롤 방지 — 배경 장식(fixed blob)이 뷰포트 밖으로 넘쳐도 가로 스크롤이 생기지 않게 한다 */
html { overflow-x: hidden; }