from sklearn.preprocessing import StandardScaler

def scale_features(X_train, X_test):
    """
    Scale features using StandardScaler.
    
    Args:
        X_train (pd.DataFrame): Training features.
        X_test (pd.DataFrame): Testing features.
        
    Returns:
        X_train_scaled, X_test_scaled: Scaled features.
    """
    scaler = StandardScaler()
    X_train_scaled = scaler.fit_transform(X_train)
    X_test_scaled = scaler.transform(X_test)
    return X_train_scaled, X_test_scaled