:root {
  --primary-color: #0d6efd;
  --bg-gradient: linear-gradient(135deg, #f5f7fa 0%, #c3cfe2 100%);
  --card-bg: rgba(255, 255, 255, 0.9);
  --btn-shadow: 0 4px 6px rgba(0, 0, 0, 0.05);
  --btn-hover-shadow: 0 6px 12px rgba(0, 0, 0, 0.1);
}

body {
  background: var(--bg-gradient);
  min-height: 100vh;
  display: flex;
  align-items: center;
  font-family: 'Segoe UI', Roboto, Helvetica, Arial, sans-serif;
}

.calculator-card {
  background: var(--card-bg);
  backdrop-filter: blur(10px);
  border: 1px solid rgba(255, 255, 255, 0.3);
  border-radius: 24px;
  box-shadow: 0 20px 40px rgba(0, 0, 0, 0.1);
  overflow: hidden;
  transition: transform 0.3s ease;
}

.calculator-card:hover {
  transform: translateY(-5px);
}

.display-container {
  background: #f8f9fa;
  padding: 20px;
  border-radius: 16px;
  margin-bottom: 20px;
  box-shadow: inset 0 2px 4px rgba(0, 0, 0, 0.05);
  height: 100px;
  display: flex;
  align-items: center;
  justify-content: flex-end;
}

#result {
  text-align: right;
  font-size: 38px;
  font-weight: 600;
  height: auto;
  border: none;
  background: transparent;
  padding: 0;
  color: #212529;
  box-shadow: none;
  width: 100%;
}

.btn-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 12px;
}

.calculator .btn {
  height: 60px;
  border-radius: 14px;
  font-size: 18px;
  font-weight: 600;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: all 0.2s ease;
  border: none;
  box-shadow: var(--btn-shadow);
}

.calculator .btn:hover {
  transform: translateY(-2px);
  box-shadow: var(--btn-hover-shadow);
}

.calculator .btn:active {
  transform: translateY(0);
}

.btn-light {
  background: #ffffff;
  color: #495057;
}

.btn-light:hover {
  background: #f1f3f5;
}

.btn-operator {
  background: #e7f1ff;
  color: var(--primary-color);
}

.btn-operator:hover {
  background: #cfe2ff;
}

.btn-action {
  background: #fff5f5;
  color: #fa5252;
}

.btn-action:hover {
  background: #ffe3e3;
}

.btn-equals {
  background: var(--primary-color);
  color: white;
  grid-column: span 1;
}

.btn-equals:hover {
  background: #0b5ed7;
  color: white;
}

.group-header {
  color: #495057;
  font-weight: 700;
  letter-spacing: 2px;
  margin-bottom: 20px;
  text-transform: uppercase;
  font-size: 1.2rem;
}

.theme-toggle-btn {
  position: fixed;
  top: 20px;
  right: 20px;
  z-index: 1000;
}

body.dark-mode {
  background: linear-gradient(135deg, #1a1a1a 0%, #2d2d2d 100%);
  color: #e0e0e0;
}

body.dark-mode .calculator-card {
  background: rgba(45, 45, 45, 0.9);
  border-color: rgba(255, 255, 255, 0.1);
}

body.dark-mode .display-container {
  background: #333333;
  color: #e0e0e0;
}

body.dark-mode #result {
  color: #e0e0e0;
}

body.dark-mode .btn-light {
  background: #444444;
  color: #e0e0e0;
}

body.dark-mode .btn-light:hover {
  background: #555555;
}

#scroll-to-calculator {
  position: fixed;
  bottom: 24px;
  right: 24px;
  width: 46px;
  height: 46px;
  border-radius: 14px;
  background: rgba(13, 110, 253, 0.15);
  color: var(--primary-color);
  border: none;
  font-size: 22px;
  font-weight: 700;
  cursor: pointer;
  opacity: 0.15;
  transform: translateY(10px);
  pointer-events: none;
  transition: all 0.3s ease;
  box-shadow: 0 8px 20px rgba(13, 110, 253, 0.15);
  backdrop-filter: blur(6px);
  z-index: 999;
}

body:hover #scroll-to-calculator {
  opacity: 0.6;
  transform: translateY(0);
  pointer-events: auto;
}

#scroll-to-calculator:hover {
  opacity: 1;
  background: var(--primary-color);
  color: white;
  transform: scale(1.05);
}

.converter-tabs {
  display: flex;
  gap: 4px;
  margin-bottom: 16px;
  background: rgba(0, 0, 0, 0.04);
  border-radius: 12px;
  padding: 4px;
}

body.dark-mode .converter-tabs {
  background: rgba(255, 255, 255, 0.06);
}

.converter-tab {
  flex: 1;
  padding: 8px 12px;
  border: none;
  border-radius: 10px;
  font-size: 13px;
  font-weight: 600;
  cursor: pointer;
  background: transparent;
  color: #6c757d;
  transition: all 0.2s ease;
}

.converter-tab:hover {
  color: var(--primary-color);
  background: rgba(13, 110, 253, 0.08);
}

.converter-tab.active {
  background: #fff;
  color: var(--primary-color);
  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.08);
}

body.dark-mode .converter-tab.active {
  background: #444;
  color: #e0e0e0;
  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.2);
}

.tab-content {
  animation: fadeIn 0.2s ease;
}

@keyframes fadeIn {
  from { opacity: 0; transform: translateY(4px); }
  to { opacity: 1; transform: translateY(0); }
}

.converter-panel {
  padding: 4px 0;
}

.converter-title {
  font-size: 15px;
  font-weight: 700;
  color: #495057;
  margin-bottom: 16px;
  text-align: center;
}

body.dark-mode .converter-title {
  color: #ccc;
}

.converter-row {
  display: flex;
  gap: 12px;
  margin-bottom: 12px;
}

.converter-field {
  flex: 1;
}

.converter-field-btn {
  flex: 0 0 auto;
  display: flex;
  align-items: flex-end;
}

.converter-label {
  display: block;
  font-size: 12px;
  font-weight: 600;
  color: #6c757d;
  margin-bottom: 4px;
  text-transform: uppercase;
  letter-spacing: 0.5px;
}

body.dark-mode .converter-label {
  color: #999;
}

.converter-btn {
  width: 100%;
  min-width: 100px;
  height: 42px;
  border-radius: 10px;
  font-weight: 600;
}

.converter-result {
  margin-top: 16px;
  padding: 14px 18px;
  background: #f8f9fa;
  border-radius: 12px;
  text-align: center;
  font-size: 22px;
  font-weight: 700;
  color: #212529;
  min-height: 52px;
  display: flex;
  align-items: center;
  justify-content: center;
  word-break: break-all;
}

body.dark-mode .converter-result {
  background: #333;
  color: #e0e0e0;
}

.converter-error {
  margin-top: 12px;
  padding: 10px 14px;
  background: #fff0f0;
  border-radius: 10px;
  text-align: center;
  font-size: 14px;
  color: #e03131;
  font-weight: 500;
}

body.dark-mode .converter-error {
  background: #3d1f1f;
  color: #ff6b6b;
}

.converter-loading {
  margin-top: 12px;
  padding: 10px 14px;
  text-align: center;
  font-size: 14px;
  color: #6c757d;
  font-weight: 500;
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
}

body.dark-mode .converter-loading {
  color: #999;
}

.spinner {
  display: inline-block;
  width: 16px;
  height: 16px;
  border: 2px solid #dee2e6;
  border-top-color: var(--primary-color);
  border-radius: 50%;
  animation: spin 0.6s linear infinite;
}

@keyframes spin {
  to { transform: rotate(360deg); }
}

.form-select, .converter-panel .form-control {
  border-radius: 10px;
  border: 1px solid #dee2e6;
  padding: 8px 12px;
  font-size: 14px;
  height: 42px;
}

body.dark-mode .form-select,
body.dark-mode .converter-panel .form-control {
  background: #444;
  border-color: #555;
  color: #e0e0e0;
}

body.dark-mode .form-select:focus,
body.dark-mode .converter-panel .form-control:focus {
  border-color: var(--primary-color);
  box-shadow: 0 0 0 2px rgba(13, 110, 253, 0.15);
}