Clear Property:

this is the codeusing float property without clear property

So what exactly does clear property do?
clear is applied to the element that comes AFTER a floated element. it basically tells the browser “Don’t allow this element to sit beside floated elements on the left/right/both — push it BELOW them.”

Counters in CSS:

CSS counters are "variables" maintained by CSS whose values can be incremented by CSS rules (to track how many times they are used). Counters let you adjust the appearance of content based on its placement in the document. CSS counters can be used for automatic numbering. For example:

1. item
2. item
   1. item
   2. item
   3. item
      1. item
      2. item
      3. item
   4. item
3. item
4. item

1. item
2. item

Units in css:

CSS has several different units for expressing a length.
Absolute Lengths:
The absolute length units are fixed and a length expressed in any of these will appear as exactly that size.
Relative Lengths:
Relative length units specify a length relative to another length property. Relative length units scale better between different rendering mediums.