body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
  margin: 0;
  padding: 0;
  background-color: var(--background-color);
  color: var(--text-color);
  transition: background-color 0.3s, color 0.3s;
}

:root {
  --background-color: #ffffff;
  --text-color: #000000;
}

[data-theme="dark"] {
  --background-color: #121212;
  --text-color: #ffffff;
}

#app {
  max-width: 800px;
  margin: 0 auto;
  padding: 20px;
}

header {
  text-align: center;
  margin-bottom: 20px;
}

nav button {
  margin: 0 5px;
  padding: 10px;
  cursor: pointer;
}

main {
  background-color: var(--background-color);
  padding: 20px;
  border-radius: 10px;
  box-shadow: 0 0 10px rgba(0, 0, 0, 0.1);
}

.date-picker {
  display: flex;
  justify-content: center;
  align-items: center;
  margin-bottom: 20px;
}

.date-picker button {
  background: none;
  border: none;
  cursor: pointer;
  font-size: 1.2em;
}

textarea {
  width: 100%;
  height: 150px;
  padding: 10px;
  margin-bottom: 10px;
  border-radius: 5px;
  border: 1px solid #ccc;
}

.hidden {
  display: none;
}

button {
  background-color: #007bff;
  color: white;
  border: none;
  padding: 10px 15px;
  border-radius: 5px;
  cursor: pointer;
}