/* Base design variables */
:root {
  --color-bg: #ffffff;
  --color-surface: #ffffff;
  --color-surface-soft: #f6f6f6;
  --color-task-surface: #fbfdff;
  --color-text: #18212f;
  --color-muted: #5b6676;
  --color-primary: #174ea6;
  --color-primary-dark: #123d80;
  --color-on-primary: #ffffff;
  --color-danger: #b42318;
  --color-border: #e5e5e5;
  --color-complete: #15803d;
  --color-focus: #b45309;
  --shadow-card: 0 1px 8px rgba(0, 0, 0, 0.08);
  --radius: 12px;
  --space-sm: 0.75rem;
  --space-md: 1rem;
  --space-lg: 1.5rem;
  --space-xl: 2rem;
  --font-main: system-ui, -apple-system, Segoe UI, Roboto, Arial, sans-serif;
}

body.dark-theme {
  --color-bg: #111827;
  --color-surface: #1f2937;
  --color-surface-soft: #273449;
  --color-task-surface: #172033;
  --color-text: #f9fafb;
  --color-muted: #d1d5db;
  --color-primary: #93c5fd;
  --color-primary-dark: #bfdbfe;
  --color-on-primary: #111827;
  --color-danger: #fca5a5;
  --color-border: #4b5563;
  --color-complete: #86efac;
  --color-focus: #fbbf24;
  --shadow-card: 0 1px 12px rgba(0, 0, 0, 0.35);
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  background: var(--color-bg);
  color: var(--color-text);
  font-family: var(--font-main);
  line-height: 1.5;
}

button,
input,
select {
  font: inherit;
}

button:focus-visible,
a:focus-visible,
input:focus-visible,
select:focus-visible {
  outline: 3px solid var(--color-focus);
  outline-offset: 3px;
}

.page-shell {
  width: min(960px, calc(100% - 2rem));
  margin: 0 auto;
}

.stack > * + * {
  margin-top: var(--space-md);
}

.skip-link {
  position: absolute;
  left: var(--space-md);
  top: var(--space-md);
  transform: translateY(-150%);
  background: var(--color-surface);
  color: var(--color-text);
  border: 1px solid var(--color-border);
  border-radius: 0.5rem;
  padding: 0.5rem 0.75rem;
  z-index: 10;
}

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

.site-header {
  padding: var(--space-md) 0;
  border-bottom: 1px solid var(--color-border);
  background: var(--color-surface);
}

main.page-shell {
  padding: var(--space-xl) 0;
}

.header-top {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-md);
}

.nav-list {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-md);
  margin: var(--space-sm) 0 0;
  padding: 0;
  list-style: none;
}

.nav-list a {
  color: var(--color-primary);
  font-weight: 700;
}

h1,
h2,
p {
  margin-top: 0;
}

h1 {
  margin-bottom: 0;
  font-size: 2rem;
  line-height: 1.15;
}

h2 {
  margin-bottom: 0;
  font-size: 1.35rem;
}

.intro {
  max-width: 650px;
  margin-bottom: 0;
  color: var(--color-muted);
  font-size: 1.05rem;
}

.app-card {
  padding: var(--space-lg);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  background: var(--color-surface);
  box-shadow: var(--shadow-card);
}

.section-heading {
  display: flex;
  flex-direction: column;
  gap: 0.35rem;
  margin-bottom: var(--space-lg);
}

.section-heading p {
  margin-bottom: 0;
  color: var(--color-muted);
}

.task-form {
  display: grid;
  gap: var(--space-md);
}

.form-field,
.tag-filter {
  display: grid;
  gap: 0.35rem;
}

label {
  color: var(--color-muted);
  font-weight: 700;
}

input,
select {
  width: 100%;
  min-height: 44px;
  padding: 0.65rem 0.75rem;
  border: 1px solid var(--color-border);
  border-radius: 10px;
  background: var(--color-surface);
  color: var(--color-text);
}

.theme-toggle,
.primary-button,
.filter-button,
.task-action {
  min-height: 42px;
  border: 1px solid var(--color-border);
  border-radius: 10px;
  cursor: pointer;
  font-weight: 800;
  transition: transform 160ms ease, border-color 160ms ease, background 160ms ease;
}

.theme-toggle {
  padding: 0.45rem 0.75rem;
  background: var(--color-surface-soft);
  color: var(--color-text);
}

.primary-button {
  background: var(--color-primary);
  color: var(--color-on-primary);
}

.primary-button:hover,
.theme-toggle:hover,
.filter-button:hover,
.task-action:hover {
  transform: translateY(-2px);
  border-color: var(--color-primary);
}

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

.error-message {
  min-height: 1.5rem;
  margin: var(--space-md) 0 0;
  color: var(--color-danger);
  font-weight: 700;
}

.filters {
  display: grid;
  gap: var(--space-md);
  margin-bottom: var(--space-lg);
}

.filter-group {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-sm);
}

.filter-button {
  background: var(--color-surface-soft);
  color: var(--color-text);
  padding: 0.5rem 0.8rem;
}

.active-filter {
  background: var(--color-primary);
  color: var(--color-on-primary);
}

.task-list {
  display: grid;
  gap: var(--space-md);
  margin: 0;
  padding: 0;
  list-style: none;
}

.task-item {
  display: grid;
  gap: var(--space-md);
  padding: var(--space-md);
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  background: var(--color-task-surface);
}

.task-details {
  display: grid;
  gap: 0.35rem;
}

.task-text {
  font-weight: 800;
}

.task-item.completed .task-text {
  color: var(--color-muted);
  text-decoration: line-through;
}

.task-tag {
  width: fit-content;
  padding: 0.2rem 0.55rem;
  border-radius: 999px;
  background: var(--color-surface-soft);
  color: var(--color-complete);
  font-size: 0.82rem;
  font-weight: 800;
  text-transform: capitalize;
}

.task-actions {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-sm);
}

.task-action {
  padding: 0.45rem 0.75rem;
  background: var(--color-surface);
  color: var(--color-text);
}

.delete-button {
  color: var(--color-danger);
}

.empty-state {
  padding: var(--space-lg);
  border: 1px dashed var(--color-border);
  border-radius: var(--radius);
  color: var(--color-muted);
  text-align: center;
}

@media (min-width: 680px) {
  .section-heading,
  .filters {
    align-items: center;
    grid-template-columns: 1fr auto;
  }

  .task-form {
    grid-template-columns: 1fr 180px auto;
    align-items: end;
  }

  .task-item {
    grid-template-columns: 1fr auto;
    align-items: center;
  }
}

@media (max-width: 600px) {
  .header-top {
    align-items: flex-start;
    flex-direction: column;
  }
}