:root {
  color-scheme: light;
  font-family: "Inter", "Helvetica Neue", Arial, sans-serif;
  --color-primary: #2563eb;
  --color-primary-dark: #1d4ed8;
  --color-secondary: #0f172a;
  --color-bg: #f4f6fb;
  --color-card: #ffffff;
  --color-border: #d9e2f1;
  --color-text: #1f2933;
  --color-muted: #52606d;
  --shadow: 0 12px 30px rgba(15, 23, 42, 0.08);
  --radius: 18px;
}

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

body {
  margin: 0;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  background: var(--color-bg);
  color: var(--color-text);
}

a {
  color: inherit;
  text-decoration: none;
}

.intro a {
  color: var(--color-primary);
  text-decoration: underline;
  text-decoration-thickness: 2px;
}

.app-header {
  background: #ffffff;
  border-bottom: 1px solid var(--color-border);
  padding: 1.2rem 1.6rem;
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  position: sticky;
  top: 0;
  z-index: 10;
}

.app-header h1 {
  font-size: 1.5rem;
  margin: 0;
}

.app-nav {
  display: flex;
  gap: 0.75rem;
  flex-wrap: wrap;
}

.app-nav a {
  padding: 0.45rem 0.9rem;
  border-radius: 999px;
  border: 1px solid transparent;
  font-weight: 600;
  transition: background 0.2s ease, color 0.2s ease, border-color 0.2s ease;
}

.app-nav a:hover,
.app-nav a:focus-visible {
  background: rgba(37, 99, 235, 0.1);
  border-color: rgba(37, 99, 235, 0.4);
  outline: none;
}

.app-nav a[aria-current="page"] {
  background: rgba(37, 99, 235, 0.15);
  border-color: rgba(37, 99, 235, 0.5);
}

.app-main {
  width: min(960px, 92vw);
  margin: 0 auto;
  padding: 2rem 0 3rem;
  display: flex;
  flex-direction: column;
  gap: 2rem;
}

.card {
  background: var(--color-card);
  border-radius: var(--radius);
  padding: 1.75rem;
  box-shadow: var(--shadow);
  display: flex;
  flex-direction: column;
  gap: 1.5rem;
}

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

.intro {
  margin: 0;
  color: var(--color-muted);
  line-height: 1.5;
}

.button-row {
  display: flex;
  flex-wrap: wrap;
  gap: 1rem;
}

button {
  cursor: pointer;
  border: none;
  border-radius: 999px;
  font-weight: 600;
  font-size: 1rem;
  padding: 0.85rem 1.8rem;
  transition: transform 0.15s ease, background 0.2s ease, box-shadow 0.2s ease;
  will-change: transform;
}

button:disabled {
  cursor: not-allowed;
  opacity: 0.55;
  transform: none;
  box-shadow: none;
}

button:focus-visible {
  outline: 3px solid rgba(37, 99, 235, 0.35);
  outline-offset: 2px;
}

.primary {
  background: var(--color-primary);
  color: #ffffff;
  box-shadow: 0 10px 20px rgba(37, 99, 235, 0.2);
}

.primary:hover:not(:disabled) {
  background: var(--color-primary-dark);
  transform: translateY(-1px);
}

.secondary {
  background: var(--color-secondary);
  color: #ffffff;
  box-shadow: 0 10px 20px rgba(15, 23, 42, 0.18);
}

.secondary:hover:not(:disabled) {
  transform: translateY(-1px);
}

.status {
  font-size: 1.05rem;
  color: var(--color-text);
  line-height: 1.6;
  background: rgba(37, 99, 235, 0.08);
  border-radius: var(--radius);
  padding: 1.1rem 1.2rem;
}

.overview {
  display: flex;
  flex-direction: column;
  gap: 1.5rem;
}

.empty-state {
  margin: 0;
  color: var(--color-muted);
  text-align: center;
}

.month-block {
  display: flex;
  flex-direction: column;
  gap: 1rem;
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  padding: 1.2rem;
  background: rgba(15, 23, 42, 0.02);
}

.month-block h3 {
  margin: 0;
  font-size: 1.2rem;
  color: var(--color-secondary);
}

.week-block {
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
  border-radius: calc(var(--radius) - 4px);
  padding: 0.9rem 1rem;
  background: #ffffff;
  border: 1px solid rgba(15, 23, 42, 0.08);
}

.week-block h4 {
  margin: 0;
  font-size: 1.05rem;
  color: var(--color-primary-dark);
}

.session-list {
  list-style: none;
  padding: 0;
  margin: 0;
  display: flex;
  flex-direction: column;
  gap: 0.6rem;
}

.session-item {
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 0.8rem;
  font-size: 0.98rem;
  color: var(--color-text);
}

.session-text {
  flex: 1 1 auto;
  min-width: 0;
}

.delete-button {
  background: #ef4444;
  color: #ffffff;
  padding: 0.55rem 1.1rem;
  font-size: 0.9rem;
  box-shadow: 0 8px 16px rgba(239, 68, 68, 0.18);
}

.delete-button:hover:not(:disabled) {
  background: #dc2626;
  transform: translateY(-1px);
}

.app-footer {
  margin-top: auto;
  padding: 1.5rem 1.6rem;
  text-align: center;
  color: var(--color-muted);
  font-size: 0.85rem;
}

@media (min-width: 768px) {
  .app-main {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
    gap: 2rem;
    align-items: stretch;
  }

  .card {
    height: 100%;
  }

  .status {
    font-size: 1.1rem;
  }
}