visitor analytics: flag counter

一、Reference

flag counter

二、Get Custom HTML

三、Modify mdBook template

3.1 Add HTML

./theme/index.hbs

<div id="bottom"> 
	<a href="https://info.flagcounter.com/42Wy"><img src="https://s01.flagcounter.com/count/42Wy/bg_FFFFFF/txt_000000/border_CCCCCC/columns_3/maxflags_9/viewers_0/labels_0/pageviews_1/flags_0/percent_0/" alt="Flag Counter" border="0"></a>
</div>   	 

3.2 Add CSS

./theme/css/general.css

#bottom{
    display: flex;
    justify-content: space-between;
    align-items: center;
}