* { box-sizing: border-box; }
body {
  margin: 0;
  font-family: system-ui, sans-serif;
  background: #f5f5f4;
  color: #1b1b1b;
}
.app-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 0.75rem 1rem;
  background: #1b1b1b;
  color: #fff;
}
.app-header a { color: #fff; text-decoration: none; font-weight: bold; }
.app-main { max-width: 480px; margin: 0 auto; padding: 1rem; }
.messages { list-style: none; padding: 0.5rem 1rem; margin: 0; background: #dff5df; }
fieldset.btn-selector {
  border: none;
  padding: 0;
  margin: 1rem 0;
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
}
fieldset.btn-selector legend { font-weight: bold; margin-bottom: 0.25rem; width: 100%; }
.btn-selector label {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: 44px;
  min-width: 44px;
  padding: 0.5rem 0.9rem;
  border: 2px solid #444;
  border-radius: 8px;
  background: #fff;
  font-size: 1rem;
  cursor: pointer;
}
.btn-selector input[type="radio"] { position: absolute; opacity: 0; pointer-events: none; }
.btn-selector input[type="radio"]:checked + label,
.btn-selector label.is-selected {
  background: #1b1b1b;
  color: #fff;
  border-color: #1b1b1b;
}
button, .btn-primary {
  min-height: 44px;
  font-size: 1.1rem;
  border-radius: 8px;
  border: none;
  background: #1b1b1b;
  color: #fff;
  padding: 0.6rem 1.2rem;
  width: 100%;
  margin-top: 1rem;
  cursor: pointer;
}
details { margin: 1rem 0; }
input[type="text"], input[type="number"], input[type="datetime-local"], select, textarea {
  width: 100%;
  min-height: 44px;
  font-size: 1rem;
  padding: 0.4rem;
  margin: 0.25rem 0 0.75rem;
}