*,
*::before,
*::after {
  box-sizing: border-box;
}

:root {
  --text-color: #333;
  --bg-color: #fff;
  --header-bg: #f8f9fa;
  --card-bg: #fff;
  --card-border: #e9ecef;
  --card-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
  --button-bg: #007bff;
  --button-hover: #0056b3;
  --input-border: #ced4da;
  --input-focus: #007bff;
  --error-color: #dc3545;

  /* Breakpoints */
  --bp-desktop: 1024px;
  --bp-tablet: 768px;
  --bp-mobile: 576px;
  --bp-small: 480px;

  /* Z-index layers */
  --z-dropdown: 100;
  --z-sticky: 200;
  --z-fixed: 300;
  --z-modal-backdrop: 400;
  --z-modal: 500;
  --z-popover: 600;
  --z-tooltip: 700;
  --z-notification: 800;
}

.page.theme-dark {
  --text-color: #e9ecef;
  --bg-color: #212529;
  --header-bg: #343a40;
  --card-bg: #343a40;
  --card-border: #495057;
  --card-shadow: 0 2px 4px rgba(0, 0, 0, 0.3);
  --button-bg: #0056b3;
  --button-hover: #004085;
  --input-border: #495057;
  --input-focus: #0056b3;
  --error-color: #dc3545;
}

html {
  font-size: 16px;
}

body {
  margin: 0;
  font-family:
    -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, 'Open Sans', 'Helvetica Neue',
    sans-serif;
  line-height: 1.5;
  color: var(--text-color, #333);
  background-color: var(--bg-color, #fff);
}

.visually-hidden {
  position: absolute;
  width: 1px;
  height: 1px;
  margin: -1px;
  padding: 0;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

.container {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 20px;
}

.header {
  background-color: var(--header-bg);
  padding: 20px 0;
  border-bottom: 1px solid var(--card-border);
}

.header__container {
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.header__title {
  margin: 0;
  font-size: 2rem;
  font-weight: 700;
  color: var(--text-color);
}

.header__tabs-counter {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 1rem;
  color: var(--text-color);
}

.header__tabs-number {
  font-weight: 700;
  color: var(--button-bg);
}

.main {
  padding: 40px 0;
  min-height: calc(100vh - 200px);
}

.cards {
  margin-bottom: 60px;
}

.cards__title {
  margin: 0 0 30px;
  font-size: 1.5rem;
  font-weight: 600;
  color: var(--text-color);
}

.cards__grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 24px;

  @media (max-width: var(--bp-desktop)) {
    grid-template-columns: repeat(2, 1fr);
    gap: 20px;
  }

  @media (max-width: var(--bp-mobile)) {
    grid-template-columns: 1fr;
    gap: 16px;
  }
}

.btn {
  background-color: var(--button-bg);
  color: white;
  border: none;
  border-radius: 6px;
  padding: 12px 24px;
  font-size: 1rem;
  font-weight: 500;
  cursor: pointer;
  transition:
    background-color 0.2s ease,
    transform 0.1s ease;
}

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

.btn:active {
  transform: translateY(1px);
}

.panel {
  background-color: var(--card-bg);
  border: 1px solid var(--card-border);
  border-radius: 8px;
  box-shadow: var(--card-shadow);
  transition: background-color 0.3s ease;
}

.title {
  margin: 0;
  color: var(--text-color);
  font-weight: 600;
}

.title--large {
  font-size: 1.5rem;
}

.title--medium {
  font-size: 1.25rem;
}

.title--small {
  font-size: 1.125rem;
}

.transition-theme {
  transition:
    background-color 0.3s ease,
    color 0.3s ease;
}

.card {
  padding: 24px;
  display: flex;
  flex-direction: column;
  height: 100%;
  transition:
    transform 0.2s ease,
    box-shadow 0.2s ease;
}

.card:hover {
  transform: translateY(-2px);
  box-shadow: 0 4px 8px rgba(0, 0, 0, 0.15);
}

.card__title {
  margin-bottom: 16px;
}

.card__description {
  margin: 0 0 24px;
  flex-grow: 1;
  line-height: 1.6;
  display: -webkit-box;
  -webkit-line-clamp: 3;
  -webkit-box-orient: vertical;
  overflow: hidden;
}

.subscription {
  padding: 32px;
}

.subscription__title {
  margin-bottom: 24px;
}

.subscription__form {
  margin-bottom: 32px;
}

.subscription__field-group {
  display: flex;
  gap: 12px;
  margin-bottom: 8px;

  @media (max-width: var(--bp-mobile)) {
    flex-direction: column;
  }
}

.subscription__email {
  flex: 1;
  padding: 12px 16px;
  border: 1px solid var(--input-border);
  border-radius: 6px;
  font-size: 1rem;
  background-color: var(--bg-color);
  color: var(--text-color);
  transition:
    border-color 0.2s ease,
    box-shadow 0.2s ease;
}

.subscription__email:focus {
  outline: none;
  border-color: var(--input-focus);
  box-shadow: 0 0 0 3px rgba(0, 123, 255, 0.1);
}

.subscription__email::placeholder {
  color: var(--text-color);
  opacity: 0.5;
}

.subscription__button {
  @media (max-width: var(--bp-mobile)) {
    width: 100%;
  }
}

.subscription__error {
  color: var(--error-color);
  font-size: 0.875rem;
  min-height: 20px;
  margin-top: 4px;
}

.subscription__subscribers {
  border-top: 1px solid var(--card-border);
  padding-top: 24px;
}

.subscription__subscribers-title {
  margin-bottom: 16px;
}

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

.subscription__subscriber-item {
  padding: 8px 0;
  border-bottom: 1px solid var(--card-border);
}

.subscription__subscriber-item:last-child {
  border-bottom: none;
}

.theme-toggle {
  background-color: var(--button-bg);
  border: none;
  cursor: pointer;
  position: fixed;
  bottom: 20px;
  right: 20px;
  border-radius: 50%;
  width: 56px;
  height: 56px;
  font-size: 1.5rem;
  box-shadow: 0 4px 8px rgba(0, 0, 0, 0.2);
  transition:
    transform 0.2s ease,
    box-shadow 0.2s ease;
  z-index: var(--z-fixed);
}

.theme-toggle:hover {
  transform: scale(1.05);
  box-shadow: 0 6px 12px rgba(0, 0, 0, 0.3);
}

.theme-toggle:active {
  transform: scale(0.95);
}

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

.card {
  animation: fadeIn 0.6s ease forwards;
}

.card:nth-child(1) {
  animation-delay: 0.1s;
}
.card:nth-child(2) {
  animation-delay: 0.2s;
}
.card:nth-child(3) {
  animation-delay: 0.3s;
}
.card:nth-child(4) {
  animation-delay: 0.4s;
}

.notification {
  position: fixed;
  top: 20px;
  left: 50%;
  transform: translateX(-50%);
  background-color: var(--button-bg);
  color: white;
  padding: 16px 24px;
  border-radius: 8px;
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.3);
  z-index: var(--z-notification);
  max-width: 400px;
  text-align: center;
  animation: fadeInDown 0.3s ease;
}

.notification--success {
  background-color: #28a745;
}

.notification__title {
  font-weight: 600;
  margin-bottom: 8px;
}

.notification__message {
  font-size: 0.9rem;
  opacity: 0.9;
}

@keyframes fadeInDown {
  from {
    transform: translateX(-50%) translateY(-20px);
    opacity: 0;
  }
  to {
    transform: translateX(-50%) translateY(0);
    opacity: 1;
  }
}

@keyframes fadeOutUp {
  from {
    transform: translateX(-50%) translateY(0);
    opacity: 1;
  }
  to {
    transform: translateX(-50%) translateY(-20px);
    opacity: 0;
  }
}

@media (max-width: var(--bp-tablet)) {
  .header__title {
    font-size: 1.5rem;
  }

  .main {
    padding: 30px 0;
  }

  .subscription {
    padding: 24px;
  }
}

@media (max-width: var(--bp-small)) {
  .container {
    padding: 0 16px;
  }

  .header {
    padding: 16px 0;
  }

  .card {
    padding: 20px;
  }

  .subscription {
    padding: 20px;
  }
}