:root {
  --background-color: hsl(0, 0%, 0%);
  --primary-color: hsl(0, 0%, 5%);
  --secondary-color: hsl(0, 0%, 10%);
  --secondary-hover-color: hsl(0, 0%, 15%);
  --light-text-color: hsl(0, 0%, 100%);
  --primary-text-color: hsl(0, 0%, 95%);
  --secondary-text-color: hsl(0, 0%, 70%);
  --border: hsl(0, 0%, 30%);

  --gradient: linear-gradient(0deg, var(--background-color) 95%, var(--primary-color));
  --gradient-hover: linear-gradient(0deg, var(--background-color), var(--primary-color));
  --highlight-color: hsl(0, 0%, 60%);
  --border-card: solid 1px var(--border);
  --shadow: 0px 2px 2px hsla(0, 0%, 0%, 0.07), 0px 4px 4px hsla(0, 0%, 0%, 0.015);

  --blue-button: #007bff;
  --blue-button-hover: #0056b3;
  --green-button: #4CAF50;
  --green-button-hover: #45a049;
}
body.light-theme {
  --background-color: hsl(0, 0%, 100%);
  --primary-color: hsl(0, 0%, 95%);
  --secondary-color: hsl(0, 0%, 90%);
  --h-text-color: hsl(0, 0%, 5%);
  --p-text-color: hsl(0, 0%, 30%);
  --border: hsl(0, 0%, 30%);
  --gradient: linear-gradient(0deg, var(--background-color) 95%, var(--primary-color));
  --gradient-hover: linear-gradient(0deg, var(--background-color), var(--primary-color));
  --highlight-color: hsl(0, 0%, 100%);
  --border-card: solid 1px var(--border);
}
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  font-family: Arial, sans-serif;
}
body {
  background-color: var(--background-color);
  display: flex;
  min-height: 100vh;
}
main {
  margin-left: 240px;
  padding: 30px;
  flex: 1;
  width: 100%;
}

.page-title {
  text-align: center;
  font-size: 20px;
  margin-bottom: 20px;
  color: var(--primary-text-color);
  background-color: var(--primary-color);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 12px 16px;
  box-shadow: var(--shadow);
}

.navigation-buttons {
  display: flex;
  justify-content: center;
  align-items: center;
  gap: 15px;
  margin-bottom: 25px;
}
.navigation-buttons button {
  background-color: var(--primary-color);
  color: var(--primary-text-color);
  font-weight: bold;
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 10px 22px;
  font-size: 15px;
  cursor: pointer;
  transition: background-color 0.3s ease, transform 0.2s ease;
  display: flex;
  align-items: center;
  justify-content: center;
  height: 42px;
  width: 140px;
  line-height: 1;
}
.navigation-buttons button:hover {
  background-color: var(--secondary-color);
  border-color: var(--border);
  transform: translateY(-2px);
}
.navigation-buttons button.active {
  background-color: var(--green-button);
  border-color: var(--green-button);
  color: var(--light-text-color);
}
.navigation-buttons button:disabled {
  opacity: 0.5;
  cursor: not-allowed;
}