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

[hidden] {
  display: none !important;
}

:root {
  --bg-gradient: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
  --calc-bg: #1c1c28;
  --display-bg: #2a2a3a;
  --expr-color: #8a8a9e;
  --result-color: #ffffff;
  --heading-color: #ffffff;
  --border-color: #3a3a4d;
  --btn-num-bg: #3a3a4d;
  --btn-num-color: #ffffff;
  --btn-num-hover: #45455a;
  --btn-func-bg: #50506a;
  --btn-func-color: #ffffff;
  --btn-func-hover: #5d5d78;
  --btn-op-bg: #f39c12;
  --btn-op-color: #ffffff;
  --btn-op-hover: #f5a623;
  --btn-sci-bg: #2f2f42;
  --btn-sci-color: #a5b4fc;
  --btn-sci-hover: #3a3a52;
  --btn-mode-bg: #413d5e;
  --btn-mode-color: #fbbf24;
  --btn-mode-hover: #4c476c;
  --btn-equal-bg: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
  --toolbar-color: #c7c7dd;
  --menu-bg: #262636;
  --menu-hover: #33334a;
  --input-bg: #2a2a3a;
  --input-color: #ffffff;
  --panel-title: #a5b4fc;
  --rel-btn-bg: #2f2f42;
  --rel-btn-color: #e5e7eb;
  --rel-btn-hover: #3a3a52;
  --shadow: 0 20px 60px rgba(0, 0, 0, 0.45);
}

body.light {
  --bg-gradient: linear-gradient(135deg, #e0e7ff 0%, #f3e8ff 100%);
  --calc-bg: #ffffff;
  --display-bg: #f1f3f9;
  --expr-color: #6b7280;
  --result-color: #111827;
  --heading-color: #111827;
  --border-color: #e5e7eb;
  --btn-num-bg: #f1f3f9;
  --btn-num-color: #111827;
  --btn-num-hover: #e5e7eb;
  --btn-func-bg: #e5e7eb;
  --btn-func-color: #111827;
  --btn-func-hover: #d1d5db;
  --btn-op-bg: #f59e0b;
  --btn-op-color: #ffffff;
  --btn-op-hover: #d97706;
  --btn-sci-bg: #eef2ff;
  --btn-sci-color: #4f46e5;
  --btn-sci-hover: #e0e7ff;
  --btn-mode-bg: #e0e7ff;
  --btn-mode-color: #4f46e5;
  --btn-mode-hover: #c7d2fe;
  --btn-equal-bg: linear-gradient(135deg, #4f46e5 0%, #7c3aed 100%);
  --toolbar-color: #6b7280;
  --menu-bg: #f4f5fa;
  --menu-hover: #e8ebf5;
  --input-bg: #f1f3f9;
  --input-color: #111827;
  --panel-title: #4f46e5;
  --rel-btn-bg: #eef2ff;
  --rel-btn-color: #111827;
  --rel-btn-hover: #e0e7ff;
  --shadow: 0 20px 60px rgba(0, 0, 0, 0.15);
}

body {
  min-height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
  background: var(--bg-gradient);
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  padding: 20px;
  transition: background 0.3s ease;
}

.app {
  width: 100%;
  display: flex;
  justify-content: center;
}

.calculator {
  position: relative;
  width: 100%;
  max-width: 520px;
  background: var(--calc-bg);
  border-radius: 28px;
  padding: 18px 20px 22px;
  box-shadow: var(--shadow);
  transition: background 0.3s ease;
}

.toolbar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 2px 4px 12px;
}

.toolbar-btn {
  background: transparent;
  border: none;
  color: var(--toolbar-color);
  font-size: 20px;
  cursor: pointer;
  padding: 6px 10px;
  border-radius: 10px;
  transition: background 0.15s ease;
}

.toolbar-btn:hover {
  background: var(--menu-hover);
}

#themeBtn {
  font-size: 14px;
  color: var(--expr-color);
  border: 1px solid var(--border-color);
}

.mode-switch {
  display: flex;
  align-items: center;
  gap: 6px;
  background: var(--menu-hover);
  border: none;
  color: var(--heading-color);
  font-size: 15px;
  font-weight: 600;
  padding: 8px 14px;
  border-radius: 999px;
  cursor: pointer;
  transition: background 0.15s ease;
}

.mode-switch:hover {
  background: var(--menu-bg);
  filter: brightness(1.1);
}

.mode-arrow {
  font-size: 11px;
  color: var(--expr-color);
}

.mode-menu {
  position: absolute;
  top: 52px;
  left: 18px;
  z-index: 20;
  background: var(--menu-bg);
  border-radius: 14px;
  padding: 6px;
  box-shadow: var(--shadow);
  min-width: 220px;
}

.mode-option {
  display: flex;
  flex-direction: column;
  gap: 2px;
  width: 100%;
  text-align: left;
  background: transparent;
  border: none;
  color: var(--heading-color);
  font-size: 15px;
  padding: 10px 14px;
  border-radius: 9px;
  cursor: pointer;
  transition: background 0.15s ease;
}

.mode-option:hover {
  background: var(--menu-hover);
}

.mode-option.active {
  background: var(--menu-hover);
}

.mode-option-name {
  font-weight: 600;
}

.mode-option-desc {
  font-size: 12px;
  color: var(--expr-color);
}

.display {
  background: var(--display-bg);
  border-radius: 16px;
  padding: 20px 22px;
  margin-bottom: 16px;
  min-height: 110px;
  display: flex;
  flex-direction: column;
  justify-content: flex-end;
  align-items: flex-end;
  transition: background 0.3s ease;
}

.expression {
  color: var(--expr-color);
  font-size: 16px;
  min-height: 22px;
  max-height: 66px;
  text-align: right;
  margin-bottom: 8px;
  max-width: 100%;
  overflow-y: auto;
  word-break: break-all;
  white-space: pre-wrap;
}

.result {
  color: var(--result-color);
  font-size: 40px;
  font-weight: 600;
  text-align: right;
  line-height: 1.2;
  word-break: break-all;
}

.panel {
  display: grid;
}

.scientific-panel {
  grid-template-columns: repeat(2, 1fr);
  gap: 8px;
  margin-bottom: 12px;
}

.main-panel {
  grid-template-columns: repeat(4, 1fr);
  gap: 10px;
}

.btn {
  border: none;
  outline: none;
  cursor: pointer;
  border-radius: 14px;
  font-weight: 500;
  transition: transform 0.1s ease, background 0.15s ease, filter 0.1s ease;
  user-select: none;
}

.btn:active {
  transform: scale(0.94);
}

.main-panel .btn {
  height: 60px;
  font-size: 20px;
}

.scientific-panel .btn {
  height: 44px;
  font-size: 14px;
}

.btn-num {
  background: var(--btn-num-bg);
  color: var(--btn-num-color);
}

.btn-num:hover {
  background: var(--btn-num-hover);
}

.btn-func {
  background: var(--btn-func-bg);
  color: var(--btn-func-color);
}

.btn-func:hover {
  background: var(--btn-func-hover);
}

.btn-op {
  background: var(--btn-op-bg);
  color: var(--btn-op-color);
}

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

.btn-equal {
  background: var(--btn-equal-bg);
  color: #ffffff;
}

.btn-equal:hover {
  filter: brightness(1.15);
}

.btn-sci {
  background: var(--btn-sci-bg);
  color: var(--btn-sci-color);
}

.btn-sci:hover {
  background: var(--btn-sci-hover);
}

.btn-mode {
  background: var(--btn-mode-bg);
  color: var(--btn-mode-color);
  font-weight: 600;
}

.btn-mode:hover {
  background: var(--btn-mode-hover);
}

.currency-panel,
.relative-panel {
  display: flex;
  flex-direction: column;
  gap: 14px;
}

.currency-title,
.relative-title {
  color: var(--panel-title);
  font-size: 14px;
  font-weight: 600;
  letter-spacing: 1px;
}

.currency-row {
  display: flex;
  gap: 10px;
  align-items: center;
}

.currency-amount {
  flex: 1;
  background: var(--input-bg);
  border: 1px solid var(--border-color);
  color: var(--input-color);
  border-radius: 12px;
  padding: 14px 16px;
  font-size: 22px;
  font-weight: 600;
  outline: none;
  min-width: 0;
}

.currency-amount:focus {
  border-color: var(--panel-title);
}

.currency-select {
  width: 110px;
  background: var(--input-bg);
  border: 1px solid var(--border-color);
  color: var(--input-color);
  border-radius: 12px;
  padding: 14px 10px;
  font-size: 15px;
  outline: none;
  cursor: pointer;
  appearance: auto;
}

.currency-swap-row {
  display: flex;
  justify-content: center;
}

.currency-swap {
  background: var(--btn-sci-bg);
  color: var(--btn-sci-color);
  border: none;
  border-radius: 999px;
  padding: 8px 18px;
  font-size: 13px;
  cursor: pointer;
  transition: background 0.15s ease;
}

.currency-swap:hover {
  background: var(--btn-sci-hover);
}

.currency-result {
  flex: 1;
  background: var(--display-bg);
  border-radius: 12px;
  padding: 14px 16px;
  font-size: 24px;
  font-weight: 700;
  color: var(--result-color);
  min-width: 0;
  word-break: break-all;
  min-height: 56px;
  display: flex;
  align-items: center;
}

.currency-note {
  color: var(--expr-color);
  font-size: 12px;
  text-align: center;
}

.currency-quick {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 8px;
}

.quick-amount {
  background: var(--btn-sci-bg);
  color: var(--btn-sci-color);
  border: none;
  border-radius: 10px;
  padding: 10px 0;
  font-size: 14px;
  cursor: pointer;
  transition: background 0.15s ease;
}

.quick-amount:hover {
  background: var(--btn-sci-hover);
}

.relative-chain {
  background: var(--display-bg);
  border-radius: 12px;
  padding: 14px 16px;
  font-size: 16px;
  color: var(--expr-color);
  min-height: 52px;
  word-break: break-all;
  display: flex;
  align-items: center;
}

.relative-result {
  background: var(--display-bg);
  border-radius: 12px;
  padding: 18px 16px;
  font-size: 32px;
  font-weight: 700;
  color: var(--result-color);
  text-align: center;
  min-height: 76px;
  display: flex;
  align-items: center;
  justify-content: center;
  word-break: break-all;
}

.relative-buttons {
  display: grid;
  grid-template-columns: repeat(5, 1fr);
  gap: 8px;
}

.rel-btn {
  background: var(--rel-btn-bg);
  color: var(--rel-btn-color);
  border: none;
  border-radius: 10px;
  padding: 12px 0;
  font-size: 14px;
  cursor: pointer;
  transition: background 0.15s ease;
}

.rel-btn:hover {
  background: var(--rel-btn-hover);
}

.relative-input-row {
  display: flex;
  gap: 8px;
}

.relative-input-row input {
  flex: 1;
  background: var(--input-bg);
  border: 1px solid var(--border-color);
  color: var(--input-color);
  border-radius: 10px;
  padding: 11px 14px;
  font-size: 14px;
  outline: none;
  min-width: 0;
}

.relative-input-row input:focus {
  border-color: var(--panel-title);
}

.rel-compute {
  background: var(--btn-op-bg);
  color: #ffffff;
  border: none;
  border-radius: 10px;
  padding: 0 20px;
  font-size: 14px;
  font-weight: 600;
  cursor: pointer;
}

.rel-compute:hover {
  background: var(--btn-op-hover);
}

.relative-actions {
  display: flex;
  gap: 8px;
}

.rel-action {
  flex: 1;
  background: var(--btn-func-bg);
  color: var(--btn-func-color);
  border: none;
  border-radius: 10px;
  padding: 11px 0;
  font-size: 14px;
  cursor: pointer;
  transition: background 0.15s ease;
}

.rel-action:hover {
  background: var(--btn-func-hover);
}

@media (max-width: 420px) {
  .calculator {
    padding: 12px 12px 16px;
  }

  .main-panel .btn {
    height: 52px;
    font-size: 18px;
  }

  .scientific-panel {
    grid-template-columns: repeat(4, 1fr);
  }

  .scientific-panel .btn {
    height: 40px;
    font-size: 13px;
  }

  .result {
    font-size: 32px;
  }

  .relative-buttons {
    grid-template-columns: repeat(5, 1fr);
    gap: 6px;
  }

  .rel-btn {
    font-size: 12px;
    padding: 10px 0;
  }

  .currency-select {
    width: 96px;
    font-size: 13px;
  }
}