Answers for "what are the valid techniques used to clear floats CSS"

what does clearfix for floats do in css

/* A clearfix is a way for an element 
to clear its child elements automatically without any additional markup.
The clearfix property is generally used in float layouts where elements 
are floated to be stacked horizontally. ... The clearfix property allows
a container to wrap its floated children.
*/

.clearfix {
  overflow: auto;
}

how to clear floats

This is the code 

.float-wrapper::after {
  content: "";
  clear: both;
  display: block;
}
---------------------------------------------------------------
Explanation:

.float-wrapper -> is some parent element that wraps the floating items

example:
<div class='float-wrapper'>
     <div class='floating-item'> </div>
     <div class='floating-item'> </div> 
     ....
 </div>

::after  adds  an element after the .float-wrapper, that 
has no content and clears floats from the both sides, making sure, 
other sections are not affected by floats