.diff-easy .badge { background: #0d3320; color: #3fb950; border: 1px solid #238636; } .diff-medium .badge { background: #3d2e00; color: #d29922; border: 1px solid #9e6a03; } .diff-hard .badge { background: #3d1114; color: #f85149; border: 1px solid #da3633; } .diff-expert .badge { background: #2a1541; color: #bc4dff; border: 1px solid #8b3dba; } .level-header h1 { font-size: 1.5rem; color: #e6edf3; margin-bottom: 0.5rem; } .defenses { font-size: 0.85rem; color: #8b949e; margin-bottom: 0.5rem; } .defenses strong { color: #c9d1d9; } .challenge-area { background: #161b22; border: 1px solid #30363d; border-radius: 12px; padding: 1.5rem; margin-bottom: 1.5rem; } form { display: flex; gap: 0.75rem; margin-bottom: 1rem; flex-wrap: wrap; } input[type="text"], textarea { flex: 1; min-width: 250px; padding: 0.6rem 1rem; background: #0d1117; border: 1px solid #30363d; border-radius: 8px; color: #c9d1d9; font-size: 0.9rem; font-family: inherit; } input[type="text"]:focus, textarea:focus { outline: none; border-color: #58a6ff; } button { padding: 0.6rem 1.5rem; background: #238636; border: 1px solid #2ea043; border-radius: 8px; color: #fff; font-size: 0.85rem; font-weight: 600; cursor: pointer; } button:hover { background: #2ea043; } .output { padding: 1rem; background: #0d1117; border: 1px solid #30363d; border-radius: 8px; min-height: 3rem; word-break: break-all; } .hint { margin-top: 1.5rem; } .hint details { background: #161b22; border: 1px solid #30363d; border-radius: 12px; padding: 1rem; } .hint summary { cursor: pointer; color: #d29922; font-weight: 600; font-size: 0.9rem; } .hint p { margin-top: 0.75rem; font-size: 0.85rem; color: #8b949e; line-height: 1.6; } .hint code { background: #21262d; padding: 0.15rem 0.4rem; border-radius: 4px; font-size: 0.8rem; color: #c9d1d9; } .writeup { display: none; margin-top: 1.5rem; background: linear-gradient(135deg, #161b22 0%, #1a1025 100%); border: 1px solid #8b3dba; border-radius: 12px; padding: 1.5rem; } .writeup h2 { font-size: 1.1rem; color: #c084fc; margin-bottom: 1rem; } .writeup h3 { font-size: 0.85rem; text-transform: uppercase; letter-spacing: 0.05em; color: #bc4dff; margin-top: 1.25rem; margin-bottom: 0.5rem; } .writeup h3:first-of-type { margin-top: 0; } .writeup p { font-size: 0.85rem; color: #c9d1d9; line-height: 1.7; } .writeup code { background: #21262d; padding: 0.15rem 0.4rem; border-radius: 4px; font-size: 0.8rem; color: #e6edf3; } .success-banner { display: none; position: fixed; top: 0; left: 0; right: 0; padding: 1rem; background: linear-gradient(135deg, #238636, #2ea043); color: #fff; text-align: center; font-weight: 700; font-size: 1.1rem; z-index: 9999; animation: slideDown 0.3s ease; align-items: center; justify-content: center; gap: 1.5rem; } .success-banner a { color: #fff; background: rgba(255,255,255,0.2); padding: 0.35rem 1rem; border-radius: 6px; text-decoration: none; font-size: 0.85rem; font-weight: 600; border: 1px solid rgba(255,255,255,0.3); } .success-banner a:hover { background: rgba(255,255,255,0.3); } @keyframes slideDown { from { transform: translateY(-100%); } to { transform: translateY(0); } }

Level 16 — Expert

Recursive Keyword Filter

Defenses: The filter runs in a loop until no more changes occur. Strips: <script>, event handlers (on*=), javascript:, alert, eval, prompt, confirm, Function. Nesting tricks won't work here.

The filter loops until clean. No nesting tricks, no keyword games. Think outside the box.

Hint (try on your own first!)

Recursive Keyword Filter

Why It Worked

Key Lesson

Real-World Application