how to active a link in html code example

Example 1: link active css

a:active {
  background-color: #34D399;
}

Example 2: active link

# Foward slash is equal to homepage. For all others you use IN keyword.
<li 
  {% if '/' == request.path %}
  	class="nav-item active mr-3"
  {% else %}
  	class="nav-item mr-3"
  {% endif %}
>

<li 
  {% if 'about' in request.path %}
      class="nav-item active mr-3"
  {% else %}
      class="nav-item mr-3"
  {% endif %}
>