:root {
  --primary-color: #4a90e2;
  --secondary-color: #6c757d;
  --success-color: #28a745;
  --background: #f8f9fa;
  --card-shadow: 0 2px 8px rgba(0, 0, 0, 0.1);
  --border-radius: 8px;
  
  /* Light theme (default) */
  --bg-gradient-start: #667eea;
  --bg-gradient-end: #764ba2;
  --card-bg: white;
  --text-color: #495057;
  --text-color-heading: white;
  --input-bg: white;
  --input-border: #e9ecef;
  --person-card-bg: white;
  --debt-item-bg: linear-gradient(to right, #f8f9fa 0%, #ffffff 100%);
  --debt-item-hover: linear-gradient(to right, #e9ecef 0%, #f8f9fa 100%);
  --secondary-text: #6c757d;
  --success-bg: linear-gradient(135deg, #28a745 0%, #20c997 100%);
  --success-shadow: rgba(40, 167, 69, 0.25);
  --amount-gradient: linear-gradient(135deg, #4a90e2 0%, #357abd 100%);
  --amount-shadow: rgba(74, 144, 226, 0.3);
}

[data-theme="dark"] {
  --primary-color: #5ba3ff;
  --secondary-color: #8e9aaf;
  --success-color: #3ddc84;
  --bg-gradient-start: #1a1a2e;
  --bg-gradient-end: #16213e;
  --card-bg: #252b48;
  --text-color: #e0e0e0;
  --text-color-heading: #ffffff;
  --input-bg: #1f2544;
  --input-border: #3a4359;
  --person-card-bg: #2c3350;
  --debt-item-bg: linear-gradient(to right, #2c3350 0%, #353d5f 100%);
  --debt-item-hover: linear-gradient(to right, #353d5f 0%, #3a4470 100%);
  --secondary-text: #9ca3af;
  --card-shadow: 0 2px 8px rgba(0, 0, 0, 0.4);
  --success-bg: linear-gradient(135deg, #3ddc84 0%, #2ecc71 100%);
  --success-shadow: rgba(61, 220, 132, 0.25);
  --amount-gradient: linear-gradient(135deg, #5ba3ff 0%, #4a8fd8 100%);
  --amount-shadow: rgba(91, 163, 255, 0.3);
}

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

body {
  background: linear-gradient(135deg, var(--bg-gradient-start) 0%, var(--bg-gradient-end) 100%);
  min-height: 100vh;
  padding: 2rem 1rem;
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
  margin: 0;
  transition: background 0.3s ease;
}

.container {
  max-width: 650px;
  margin: 0 auto;
  padding: 0 1rem;
}

.logo-container {
  display: inline-flex;
  justify-content: center;
  align-items: center;
  gap: 0.75rem;
  margin-bottom: 2.5rem;
  padding-top: 1rem;
}

.logo {
  width: 60px;
  height: 60px;
  filter: drop-shadow(0 4px 8px rgba(0, 0, 0, 0.2));
  display: block;
}

.logo-text {
  color: var(--text-color-heading);
  font-size: 1.75rem;
  font-weight: 700;
  letter-spacing: 0.15em;
  text-shadow: 2px 2px 4px rgba(0, 0, 0, 0.2);
  text-transform: uppercase;
}

.logo-text-container {
  display: flex;
  align-items: flex-end;
  gap: 0.25rem;
}

.logo-version {
  color: var(--text-color-heading);
  font-size: 0.75rem;
  font-weight: 600;
  opacity: 0.8;
  padding-bottom: 0.15rem;
}

.header-controls {
  display: flex;
  justify-content: center;
  align-items: center;
  gap: 1rem;
  margin-bottom: 2rem;
  flex-wrap: wrap;
}

.language-selector {
  display: flex;
  justify-content: center;
  gap: 0.5rem;
  padding-right: 1rem;
  border-right: 2px solid rgba(255, 255, 255, 0.3);
}

.theme-toggle {
  background: rgba(255, 255, 255, 0.2);
  color: white;
  border: 2px solid rgba(255, 255, 255, 0.3);
  padding: 0.5rem;
  border-radius: 50%;
  width: 40px;
  height: 40px;
  font-size: 1.2rem;
  cursor: pointer;
  transition: all 0.2s;
  backdrop-filter: blur(10px);
  display: flex;
  align-items: center;
  justify-content: center;
}

.theme-toggle:hover {
  background: rgba(255, 255, 255, 0.3);
  border-color: rgba(255, 255, 255, 0.5);
  transform: rotate(15deg);
}

.theme-icon {
  display: block;
  line-height: 1;
}

.lang-btn {
  background: rgba(255, 255, 255, 0.2);
  color: white;
  border: 2px solid rgba(255, 255, 255, 0.3);
  padding: 0.5rem 1rem;
  border-radius: 20px;
  font-weight: 600;
  font-size: 0.9rem;
  cursor: pointer;
  transition: all 0.2s;
  backdrop-filter: blur(10px);
}

.lang-btn:hover {
  background: rgba(255, 255, 255, 0.3);
  border-color: rgba(255, 255, 255, 0.5);
  transform: translateY(-2px);
}

.lang-btn.active {
  background: white;
  color: var(--primary-color);
  border-color: white;
}

.card {
  background: var(--card-bg);
  border-radius: var(--border-radius);
  box-shadow: var(--card-shadow);
  padding: 2rem;
  margin-bottom: 1rem;
  transition: background 0.3s ease;
}

h1 {
  color: var(--text-color-heading);
  font-weight: 500;
  margin-top: 0;
  margin-bottom: 2rem;
  text-align: center;
  text-shadow: 1px 1px 3px rgba(0, 0, 0, 0.15);
  font-size: 1.5rem;
  opacity: 0.9;
}

.person-input {
  display: flex;
  gap: 0.75rem;
  margin-bottom: 1rem;
  align-items: center;
}

.person-input input {
  flex: 1;
  padding: 0.75rem;
  border: 2px solid var(--input-border);
  border-radius: var(--border-radius);
  font-size: 1rem;
  transition: border-color 0.2s, background 0.3s ease, color 0.3s ease;
  background: var(--input-bg);
  color: var(--text-color);
}

.person-input input:focus {
  outline: none;
  border-color: var(--primary-color);
}

.person-input input[type="number"] {
  max-width: 150px;
}

.remove-btn {
  background: transparent;
  color: #dc3545;
  border: 2px solid #dc3545;
  border-radius: 50%;
  width: 28px;
  height: 28px;
  font-size: 1.3rem;
  font-weight: 300;
  cursor: pointer;
  transition: all 0.2s;
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
  padding: 0;
  padding-bottom: 2px;
  opacity: 0.6;
}

.remove-btn.hidden {
  display: none;
}

.remove-btn:hover {
  background: #dc3545;
  color: white;
  border-color: #dc3545;
  opacity: 1;
  transform: scale(1.1);
  box-shadow: 0 2px 8px rgba(220, 53, 69, 0.4);
}

.btn-group {
  display: flex;
  gap: 0.75rem;
  margin-top: 1.5rem;
}

.btn {
  flex: 1;
  padding: 0.875rem;
  border: none;
  border-radius: var(--border-radius);
  font-size: 1rem;
  font-weight: 600;
  cursor: pointer;
  transition: all 0.2s;
}

.btn-secondary {
  background: var(--secondary-color);
  color: white;
}

.btn-secondary:hover {
  background: #5a6268;
  transform: translateY(-2px);
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.15);
}

.btn-primary {
  background: var(--primary-color);
  color: white;
}

.btn-primary:hover {
  background: #357abd;
  transform: translateY(-2px);
  box-shadow: 0 4px 12px rgba(74, 144, 226, 0.4);
}

/* Input validation shake */
@keyframes shake {
  0%, 100% { transform: translateX(0); }
  20% { transform: translateX(-6px); }
  40% { transform: translateX(6px); }
  60% { transform: translateX(-4px); }
  80% { transform: translateX(4px); }
}

.person-input input.invalid {
  border-color: #dc3545;
  animation: shake 0.4s ease;
}

/* Contribution Breakdown */
.contributions-section {
  margin-bottom: 1.75rem;
}

.contributions-title {
  font-size: 0.75rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--secondary-text);
  opacity: 0.75;
  margin-bottom: 0.875rem;
}

.contribution-item {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  margin-bottom: 0.625rem;
  font-size: 0.9rem;
}

.contribution-name {
  color: var(--text-color);
  font-weight: 600;
  min-width: 80px;
  flex-shrink: 0;
}

.contribution-bar-wrapper {
  flex: 1;
  height: 8px;
  background: var(--input-border);
  border-radius: 4px;
  overflow: hidden;
  position: relative;
}

.contribution-bar {
  height: 100%;
  border-radius: 4px;
  transition: width 0.6s cubic-bezier(0.4, 0, 0.2, 1);
  min-width: 2px;
}

.contribution-bar.overpaid {
  background: var(--success-color);
}

.contribution-bar.underpaid {
  background: #dc3545;
}

.contribution-bar.even {
  background: var(--secondary-text);
  opacity: 0.5;
}

.contribution-diff {
  font-size: 0.8rem;
  font-weight: 600;
  min-width: 80px;
  text-align: right;
  white-space: nowrap;
}

.contribution-diff.positive {
  color: var(--success-color);
}

.contribution-diff.negative {
  color: #dc3545;
}

.contribution-diff.neutral {
  color: var(--secondary-text);
  opacity: 0.7;
}

/* Share button */
.share-btn {
  display: flex;
  align-items: center;
  gap: 0.375rem;
  padding: 0.5rem 0.875rem;
  background: transparent;
  color: var(--secondary-text);
  border: 1.5px solid var(--input-border);
  border-radius: 8px;
  font-size: 0.8rem;
  font-weight: 600;
  cursor: pointer;
  transition: all 0.2s ease;
  white-space: nowrap;
}

.share-btn:hover {
  background: var(--primary-color);
  color: white;
  border-color: var(--primary-color);
  transform: translateY(-1px);
  box-shadow: 0 3px 10px rgba(74, 144, 226, 0.3);
}

.share-btn svg {
  width: 14px;
  height: 14px;
  flex-shrink: 0;
}

.summary-actions {
  display: flex;
  gap: 0.5rem;
}

#summary {
  margin-top: 2rem;
  padding-top: 1.25rem;
  animation: fadeIn 0.4s ease-out;
}

/* Summary Header with title + copy button */
.summary-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 1.5rem;
}

.summary-header h4 {
  margin-bottom: 0 !important;
}

/* Copy Summary Button */
.copy-summary-btn {
  display: flex;
  align-items: center;
  gap: 0.375rem;
  padding: 0.5rem 0.875rem;
  background: transparent;
  color: var(--secondary-text);
  border: 1.5px solid var(--input-border);
  border-radius: 8px;
  font-size: 0.8rem;
  font-weight: 600;
  cursor: pointer;
  transition: all 0.2s ease;
  white-space: nowrap;
}

.copy-summary-btn:hover {
  background: var(--primary-color);
  color: white;
  border-color: var(--primary-color);
  transform: translateY(-1px);
  box-shadow: 0 3px 10px rgba(74, 144, 226, 0.3);
}

.copy-summary-btn.copied {
  background: var(--success-color);
  color: white;
  border-color: var(--success-color);
}

.copy-summary-btn svg {
  width: 14px;
  height: 14px;
  flex-shrink: 0;
}

/* Stats Overview Bar */
.stats-bar {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 0.75rem;
  margin-bottom: 1.75rem;
  animation: fadeIn 0.4s ease-out;
}

.stat-item {
  background: var(--debt-item-bg);
  border-radius: 10px;
  padding: 1rem 0.75rem;
  text-align: center;
  border: 1px solid var(--input-border);
  transition: all 0.3s ease;
}

.stat-item:hover {
  transform: translateY(-2px);
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.08);
}

.stat-value {
  font-size: 1.25rem;
  font-weight: 700;
  color: var(--primary-color);
  display: block;
  margin-bottom: 0.25rem;
}

.stat-label {
  font-size: 0.7rem;
  font-weight: 600;
  color: var(--secondary-text);
  text-transform: uppercase;
  letter-spacing: 0.08em;
  opacity: 0.8;
}

/* Summary Divider */
.summary-divider {
  height: 1px;
  background: linear-gradient(to right, transparent, var(--input-border), transparent);
  margin: 1.5rem 0;
}

@keyframes fadeIn {
  from {
    opacity: 0;
    transform: translateY(10px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

#summary h4 {
  color: var(--text-color);
  font-weight: 600;
  margin-top: 0;
  margin-bottom: 1.75rem;
  font-size: 1rem;
  text-align: left;
  padding-bottom: 0;
  border-bottom: none;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  opacity: 0.75;
}

.person-card {
  background: var(--person-card-bg);
  border-radius: 12px;
  padding: 1.75rem;
  margin-bottom: 1.5rem;
  border: 1px solid var(--input-border);
  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.04);
  transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
  position: relative;
  overflow: hidden;
  animation: slideUp 0.4s ease-out both;
}

.person-card:nth-child(2) { animation-delay: 0.08s; }
.person-card:nth-child(3) { animation-delay: 0.16s; }
.person-card:nth-child(4) { animation-delay: 0.24s; }
.person-card:nth-child(5) { animation-delay: 0.32s; }
.person-card:nth-child(6) { animation-delay: 0.40s; }

@keyframes slideUp {
  from {
    opacity: 0;
    transform: translateY(20px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

.person-card::before {
  content: '';
  position: absolute;
  left: 0;
  top: 0;
  bottom: 0;
  width: 4px;
  background: var(--primary-color);
  border-radius: 12px 0 0 12px;
  transition: width 0.3s ease;
}

.person-card:hover {
  transform: translateY(-3px);
  box-shadow: 0 8px 24px rgba(0, 0, 0, 0.12);
  border-color: var(--primary-color);
}

.person-card:hover::before {
  width: 6px;
}

.person-name {
  color: var(--text-color);
  font-weight: 600;
  font-size: 1.05rem;
  margin-bottom: 1.25rem;
  display: flex;
  align-items: center;
  gap: 0.625rem;
  padding-bottom: 0.75rem;
  border-bottom: 1px solid var(--input-border);
}

.person-name .name-highlight {
  color: var(--primary-color);
  font-size: 1.125rem;
  font-weight: 700;
}

.person-name .pays-label {
  color: var(--secondary-text);
  font-size: 0.9rem;
  font-weight: 500;
}

.payment-label {
  color: var(--secondary-text);
  font-size: 0.75rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.12em;
  margin-bottom: 0.875rem;
  display: flex;
  align-items: center;
  gap: 0.375rem;
  opacity: 0.7;
}

.debt-list {
  list-style: none;
  padding: 0;
  margin: 0;
}

.debt-item {
  background: var(--debt-item-bg);
  padding: 1rem 1.25rem;
  margin-bottom: 0.625rem;
  border-radius: 10px;
  display: flex;
  justify-content: space-between;
  align-items: center;
  border: 1px solid transparent;
  transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

.debt-item:hover {
  background: var(--debt-item-hover);
  border-color: var(--input-border);
  transform: translateX(6px);
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.08);
}

.debt-item:last-child {
  margin-bottom: 0;
}

.debt-recipient {
  color: var(--text-color);
  font-weight: 500;
  display: flex;
  align-items: center;
  gap: 0.625rem;
  font-size: 0.95rem;
  flex: 1;
}

.pay-to {
  color: var(--secondary-text);
  font-weight: 500;
  font-size: 0.75rem;
  margin-right: 0.375rem;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  opacity: 0.7;
}

.debt-recipient::before {
  content: '→';
  color: var(--primary-color);
  font-weight: 700;
  font-size: 1.25rem;
  transition: transform 0.3s ease;
}

.debt-item:hover .debt-recipient::before {
  transform: translateX(3px);
}

.debt-amount {
  background: var(--amount-gradient);
  color: white;
  font-weight: 700;
  font-size: 1rem;
  padding: 0.625rem 1.125rem;
  border-radius: 24px;
  box-shadow: 0 3px 10px var(--amount-shadow);
  white-space: nowrap;
  letter-spacing: 0.02em;
  transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
  position: relative;
  overflow: hidden;
}

.debt-amount::before {
  content: '';
  position: absolute;
  top: 0;
  left: -100%;
  width: 100%;
  height: 100%;
  background: linear-gradient(90deg, transparent, rgba(255, 255, 255, 0.2), transparent);
  transition: left 0.5s ease;
}

.debt-item:hover .debt-amount {
  transform: scale(1.05);
  box-shadow: 0 4px 16px var(--amount-shadow);
}

.debt-item:hover .debt-amount::before {
  left: 100%;
}

.no-debts {
  text-align: center;
  padding: 2.5rem 2rem;
  background: var(--success-bg);
  border-radius: 12px;
  color: white;
  font-size: 1.125rem;
  font-weight: 600;
  box-shadow: 0 4px 20px var(--success-shadow);
  animation: celebrate 0.6s ease-out;
  position: relative;
  overflow: hidden;
}

.no-debts::before {
  content: '✓';
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  font-size: 8rem;
  opacity: 0.1;
  font-weight: 700;
}

@keyframes bounce {
  0%, 100% { transform: translateY(0); }
  50% { transform: translateY(-10px); }
}

@keyframes celebrate {
  0% {
    transform: scale(0.8);
    opacity: 0;
  }
  50% {
    transform: scale(1.05);
  }
  100% {
    transform: scale(1);
    opacity: 1;
  }
}

.hidden {
  display: none;
}

.footer {
  text-align: center;
  padding: 1.5rem 1rem;
  margin-top: 2rem;
}

.github-link {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  color: rgba(255, 255, 255, 0.9);
  text-decoration: none;
  font-size: 0.95rem;
  font-weight: 500;
  padding: 0.625rem 1.25rem;
  background: rgba(255, 255, 255, 0.15);
  border-radius: 25px;
  backdrop-filter: blur(10px);
  border: 1px solid rgba(255, 255, 255, 0.2);
  transition: all 0.2s;
}

.github-link:hover {
  background: rgba(255, 255, 255, 0.25);
  border-color: rgba(255, 255, 255, 0.4);
  transform: translateY(-2px);
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.2);
}

.github-icon {
  flex-shrink: 0;
}

@media (max-width: 576px) {
  body {
    padding: 1rem 0.5rem;
  }
  
  .card {
    padding: 1.5rem;
  }
  
  .person-input {
    gap: 0.5rem;
  }
  
  .person-input input[type="text"] {
    flex: 2;
    min-width: 0;
  }
  
  .person-input input[type="number"] {
    flex: 1;
    max-width: none;
    min-width: 0;
  }
  
  .remove-btn {
    width: 32px;
    height: 32px;
    font-size: 1rem;
  }
  
  .btn-group {
    flex-direction: column;
  }

  .stats-bar {
    grid-template-columns: 1fr;
    gap: 0.5rem;
  }

  .stat-item {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 0.75rem 1rem;
    text-align: left;
  }

  .stat-value {
    font-size: 1.1rem;
    margin-bottom: 0;
    order: 2;
  }

  .stat-label {
    order: 1;
  }

  .summary-header {
    flex-wrap: wrap;
    gap: 0.75rem;
  }

  .person-card {
    padding: 1.25rem;
  }

  .debt-amount {
    padding: 0.5rem 0.875rem;
    font-size: 0.9rem;
  }
}