e & CORS</h6>
                        <p class="small text-muted">Custom middleware and rate limiting</p>
                        <div class="difficulty intermediate">Intermediate</div>
                    </div>
                </div>
                
                <div class="col-md-6 col-lg-3">
                    <div class="challenge-card">
                        <div class="challenge-number">3</div>
                        <h6>Validation & Errors</h6>
                        <p class="small text-mu