/* Общие стили */
:root {
  --primary: #4a90e2;
  --primary-hover: #357abd;
  --secondary: #8e8e93;
  --secondary-hover: #747479;
  --text-primary: #333333;
  --text-secondary: #666666;
  --text-inverse: #fbfbfb;
  --bg-primary: #fbfbfb;
  --bg-secondary: #f5f5f5;
  --bg-tertiary: #f0f0f0;
  --border: #e0e0e0;
  --border-strong: #d0d0d0;
  --shadow: rgba(0, 0, 0, 0.08);
  --shadow-tt: #b1b1b1;
  --error: #d32f2f;
  --page-background: linear-gradient(135deg, #c6e7ff, #ffddae);
  --surface-background: radial-gradient(circle at 0% 0%, rgba(198, 231, 255, 0.58) 0%, rgba(251, 251, 251, 0.94) 72%);
  --surface-shadow: 0 20px 50px rgba(74, 144, 226, 0.16), 0 8px 20px rgba(0, 0, 0, 0.08);
  --control-background: rgba(251, 251, 251, 0.82);
  --focus-ring: rgba(74, 144, 226, 0.3);
  --selection-background: rgba(74, 144, 226, 0.24);
  --scrollbar-track: #f5f5f5;
  --scrollbar-thumb: #d0d0d0;
}

body.dark-theme {
  --primary: #90caf9;
  --primary-hover: #64b5f6;
  --secondary: #ce93d8;
  --secondary-hover: #ba68c8;
  --text-primary: #e0e0e0;
  --text-secondary: #b0b0b0;
  --text-inverse: #121212;
  --bg-primary: #121212;
  --bg-secondary: #1e1e1e;
  --bg-tertiary: #282828;
  --border: #333333;
  --border-strong: #404040;
  --shadow: rgba(0, 0, 0, 0.3);
  --error: #f44336;
  --page-background: linear-gradient(292deg, hsl(210 68% 26%), hsla(0 0% 0% / 0.95));
  --surface-background: radial-gradient(circle at 0% 0%, hsla(210 100% 23% / 0.2) 0%, var(--bg-primary) 72%);
  --surface-shadow: 20px 20px 50px rgba(0, 0, 0, 0.3), -20px -20px 50px #121212;
  --control-background: rgba(18, 18, 18, 0.88);
  --focus-ring: rgba(144, 202, 249, 0.28);
  --selection-background: rgba(144, 202, 249, 0.28);
  --scrollbar-track: #1e1e1e;
  --scrollbar-thumb: #404040;
}

* {
  box-sizing: border-box;
}

body {
  font-family:
    'Inter',
    -apple-system,
    BlinkMacSystemFont,
    'Segoe UI',
    Roboto,
    Oxygen,
    Ubuntu,
    Cantarell,
    sans-serif;
  margin: 0;
  padding: 0;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  justify-content: flex-start;
  align-items: center;
  background: var(--page-background);
  background-attachment: fixed;
  color: var(--text-primary);
  line-height: 1.5;
  transition:
    background-color 0.3s ease,
    color 0.3s ease;
}

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

.controls .language-menu {
  order: 1;
}
.controls #theme-toggle {
  order: 2;
}

.app-header {
  position: sticky;
  top: 0;
  z-index: 100;
  width: 100%;
  min-height: 70px;
  padding: 0.7rem max(1rem, calc((100% - 1200px) / 2));
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  border-bottom: 1px solid var(--border);
  background: color-mix(in srgb, var(--control-background) 88%, transparent);
  backdrop-filter: blur(18px);
  -webkit-backdrop-filter: blur(18px);
}

.app-brand {
  flex: 1 1 55%;
  min-width: 0;
  display: flex;
  align-items: center;
  gap: 0.65rem;
  color: var(--text-primary);
  text-decoration: none;
  font-weight: 800;
}
.app-brand span {
  overflow: hidden;
  white-space: nowrap;
  text-overflow: ellipsis;
}
.app-brand img {
  width: 36px;
  height: 36px;
  border-radius: 10px;
  box-shadow: 0 8px 22px var(--shadow);
}
.language-menu {
  position: relative;
}
.language-menu__trigger {
  min-width: 140px;
  min-height: 44px;
  padding: 0.35rem 0.65rem 0.35rem 0.35rem;
  display: grid;
  grid-template-columns: auto 1fr auto;
  align-items: center;
  gap: 0.5rem;
  border: 1px solid var(--border);
  border-radius: 12px;
  background: var(--control-background);
  color: var(--text-primary);
  box-shadow: 0 8px 24px var(--shadow);
  font: inherit;
  font-weight: 700;
  text-align: left;
  cursor: pointer;
}
.language-menu__flag {
  width: 1.75rem;
  height: 1.75rem;
  display: grid;
  place-items: center;
  border: 1px solid var(--border);
  border-radius: 8px;
  color: var(--primary);
  font-size: 0.65rem;
  letter-spacing: 0.04em;
}
.language-menu__chevron {
  width: 1rem;
  height: 1rem;
  transform: rotate(180deg);
  transform-origin: center;
  transition: transform 240ms cubic-bezier(0.34, 1.56, 0.64, 1);
}
.language-menu__trigger[aria-expanded='true'] .language-menu__chevron {
  transform: rotate(0deg);
}
.language-menu__panel {
  position: absolute;
  top: calc(100% + 0.5rem);
  right: 0;
  width: min(210px, calc(100vw - 1rem));
  padding: 0.4rem;
  display: grid;
  gap: 0.2rem;
  border: 1px solid var(--border);
  border-radius: 14px;
  background: var(--control-background);
  box-shadow: 0 20px 44px var(--shadow);
}
.language-menu__panel[hidden] {
  display: none;
}
.language-menu__option {
  width: 100%;
  min-height: 44px;
  display: grid;
  grid-template-columns: auto 1fr auto;
  align-items: center;
  gap: 0.5rem;
  border: 1px solid transparent;
  border-radius: 10px;
  background: transparent;
  color: var(--text-primary);
  font: inherit;
  font-weight: 700;
  text-align: left;
  cursor: pointer;
}
.language-menu__option:hover,
.language-menu__option:focus-visible,
.language-menu__option[aria-checked='true'] {
  border-color: var(--border);
  background: var(--surface-background);
}
.language-menu__check {
  opacity: 0;
}
.language-menu__option[aria-checked='true'] .language-menu__check {
  opacity: 1;
}

.icon-button {
  width: 44px;
  height: 44px;
  min-width: 44px;
  border: 1px solid var(--border);
  cursor: pointer;
  padding: 8px;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--text-primary);
  background: var(--control-background);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  box-shadow: 0 8px 24px var(--shadow);
  transition:
    transform 0.2s ease,
    box-shadow 0.2s ease,
    border-color 0.2s ease,
    background-color 0.2s ease;
}

.icon-button:hover {
  transform: translateY(-2px);
  border-color: var(--primary);
  box-shadow: 0 12px 30px var(--shadow);
}

.icon-button:active {
  transform: translateY(0);
}

/* Контейнер */
.container {
  margin: clamp(1rem, 5vw, 4rem) auto;
  background: var(--surface-background);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  padding: 2.5rem;
  border-radius: 16px;
  box-shadow: var(--surface-shadow);
  max-width: 800px;
  width: 100%;
  margin: 2rem;
  border: 1px solid var(--border);
  transition:
    background-color 0.3s ease,
    border-color 0.3s ease,
    box-shadow 0.1s ease;
}

/* Заголовок */
.header h1 {
  font-size: 2rem;
  color: var(--text-primary);
  text-align: center;
  margin-bottom: 2rem;
  font-weight: 600;
  transition: color 0.3s ease;
}

/* Секция калькулятора */
.calculator-section {
  margin-bottom: 2.5rem;
}

#calculator {
  display: flex;
  flex-direction: column;
  gap: 1.5rem;
}

.form-group {
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
}

.form-group label {
  font-weight: 500;
  color: var(--text-primary);
  font-size: 0.95rem;
  transition: color 0.3s ease;
}

.form-group input {
  width: 100%;
  padding: 0.875rem 1rem;
  border: 1px solid var(--border);
  border-radius: 8px;
  font-size: 1rem;
  background-color: var(--bg-primary);
  color: var(--text-primary);
  transition:
    border-color 0.3s ease,
    box-shadow 0.3s ease,
    background-color 0.3s ease,
    color 0.3s ease;
}

.form-group input:focus {
  border-color: var(--primary);
  box-shadow: 0 0 0 3px var(--focus-ring);
  outline: none;
}

/* Группа кнопок */
.button-group {
  display: flex;
  gap: 1rem;
  justify-content: center;
  margin-top: 1.5rem;
}

button {
  padding: 0.875rem 1.75rem;
  border: none;
  border-radius: 8px;
  font-size: 1rem;
  font-weight: 500;
  cursor: pointer;
  transition: all 0.3s ease;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-width: 120px;
}

button.primary {
  background-color: var(--primary);
  color: var(--text-inverse);
  box-shadow: 0 4px 14px var(--focus-ring);
}

button.primary:hover {
  background-color: var(--primary-hover);
  box-shadow: 0 8px 22px var(--focus-ring);
  transform: translateY(-2px);
}

button.primary:active {
  transform: translateY(0);
}

button.secondary {
  background: var(--control-background);
  color: var(--primary);
  border: 1px solid var(--primary);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
}

button.secondary:hover {
  background-color: var(--bg-secondary);
  transform: translateY(-2px);
}

button.secondary:active {
  transform: translateY(0);
}

/* Секция результата */
.result-section {
  text-align: center;
  margin-top: 2rem;
}

.result-section h2 {
  font-size: 1.5rem;
  color: var(--text-primary);
  margin-bottom: 1.5rem;
  font-weight: 600;
  transition: color 0.3s ease;
}

.formula {
  font-size: 1.1rem;
  color: var(--primary);
  margin-bottom: 2rem;
  word-wrap: break-word;
  padding: 1rem;
  background-color: var(--bg-secondary);
  border-radius: 8px;
  font-family: 'Roboto Mono', monospace;
  transition:
    background-color 0.3s ease,
    color 0.3s ease;
}

canvas {
  border: 1px solid var(--border);
  border-radius: 8px;
  box-shadow: 0 4px 12px var(--shadow);
  max-width: 100%;
  background-color: var(--bg-primary);
  transition:
    border-color 0.3s ease,
    box-shadow 0.3s ease,
    background-color 0.3s ease;
}

.error {
  color: var(--error);
  font-weight: 500;
}

@media (max-width: 768px) {
  .container {
    padding: 1.5rem;
    margin: 1rem;
  }

  .button-group {
    flex-direction: column;
  }

  button {
    width: 100%;
  }
}

/* Theme baseline: local, dependency-free, and motion-aware. */
html {
  background-color: var(--bg-secondary);
  color-scheme: light;
  scrollbar-gutter: stable;
}

html[data-theme='dark'] {
  background-color: #121212;
  color-scheme: dark;
}

body {
  accent-color: var(--primary);
}

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

:where(a, button, input, textarea, select, summary, [tabindex]):focus-visible {
  outline: 3px solid var(--primary);
  outline-offset: 3px;
}

.skip-link {
  position: fixed;
  top: 0.75rem;
  left: 0.75rem;
  z-index: 200;
  padding: 0.75rem 1rem;
  border: 1px solid var(--border);
  border-radius: 8px;
  background: var(--bg-primary);
  color: var(--text-primary);
  box-shadow: 0 8px 24px var(--shadow);
  transform: translateY(-160%);
  transition: transform 0.2s ease;
}

.skip-link:focus {
  transform: translateY(0);
}

* {
  scrollbar-width: thin;
  scrollbar-color: var(--scrollbar-thumb) var(--scrollbar-track);
}

*::-webkit-scrollbar {
  width: 10px;
  height: 10px;
}

*::-webkit-scrollbar-track,
*::-webkit-scrollbar-corner {
  background: var(--scrollbar-track);
}

*::-webkit-scrollbar-thumb {
  min-width: 36px;
  min-height: 36px;
  border: 2px solid var(--scrollbar-track);
  border-radius: 999px;
  background: var(--scrollbar-thumb);
  background-clip: padding-box;
}

*::-webkit-scrollbar-thumb:hover {
  background: var(--primary);
  background-clip: padding-box;
}

@media (max-width: 768px) {
  .container {
    width: calc(100% - 2rem);
  }
}

@media (max-width: 480px) {
  .app-header {
    padding: 0.55rem;
    gap: 0.5rem;
  }
  .app-brand {
    gap: 0.5rem;
  }
  .app-brand img {
    width: 32px;
    height: 32px;
  }
  .language-menu__trigger {
    min-width: 54px;
    width: 54px;
    grid-template-columns: 1fr auto;
    padding: 0.3rem;
  }
  .language-menu__label {
    display: none;
  }
}

@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    scroll-behavior: auto !important;
    transition-duration: 0.01ms !important;
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
  }
}

@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    scroll-behavior: auto !important;
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
  }
}

.skip-link {
  position: fixed;
  top: 0.75rem;
  left: 0.75rem;
  z-index: 1000;
  transform: translateY(-180%);
  padding: 0.7rem 1rem;
  border: 1px solid #90caf9;
  border-radius: 10px;
  background: #111722;
  color: #e7edf7;
}

.skip-link:focus {
  transform: translateY(0);
}