def utilization_graph(utilization, warning_threshold=75, danger_threshold=90):
    """
    Display a horizontal bar graph indicating a percentage of utilization.
    """
    if utilization == 100:
        bar_class = 'bg-secondary'
    elif danger_threshold and utilization >= danger_threshold:
        bar_class = 'bg-danger'
    elif warning_threshold and utilization >= warning_threshold:
        bar_class = 'bg-warning'
    elif warning_threshold or danger_threshold:
        bar_class = 'bg-success'
    else:
        bar_class = 'bg-gray'
    return {
        'utilization': utilization,
        'bar_class': bar_class,
    }