HTML Ordered lists custom marker using CSS and `:before` pseudo-class

ordered-lists.less

ol {
    counter-reset: custom-counter-name; // any name, use afterwards for incrementing counter
    // counter-reset: custom-counter-name 1; // can be started from custom index
    
    li{
        list-style:none;
        counter-increment: custom-counter-name;
    }
    li:before {
        content: "[" counter(custom-counter-name) "]";
    }
}