body { font-family: sans-serif; background-color: #f4f4f9; color: #333; display: flex; justify-content: center; align-items: center; min-height: 100vh; margin: 0; }
.challenge-container { background: #fff; padding: 2rem; border-radius: 8px; box-shadow: 0 4px 15px rgba(0,0,0,0.1); text-align: center; max-width: 600px; width: 90%; }
h1 { color: #005A9C; } h2 { color: #444; }
.button { background-color: #007bff; color: white; padding: 10px 20px; border: none; border-radius: 5px; text-decoration: none; font-size: 16px; cursor: pointer; display: inline-block; margin-top: 10px; }
.button:hover { background-color: #0056b3; }
.start-button { background-color: #28a745; font-size: 1.2rem; padding: 15px 30px; }
.start-button:hover { background-color: #218838; }
input[type="number"] { font-size: 1rem; padding: 8px; margin: 10px 0; width: 60%; }
#feedback { font-weight: bold; min-height: 1.2em; }
table { width: 100%; margin-top: 20px; border-collapse: collapse; }
th, td { padding: 12px; border: 1px solid #ddd; }
th { background-color: #007bff; color: white; }