Best way to project, plan and structure an app with CI

My approach is top down and to create the basic tree menu system ensuring stylesheets and JavaScript files are all included.

I also use this common footer which consists of two w3.org validation service links. This dynamic script saves opening, copying, pasting, testing, the same links umpteen times.

PHP Code:

<?php 
declare(strict_types=1);

  $url    = $_SERVER['REQUEST_SCHEME'] 
          . '://'
          . $_SERVER['SERVER_NAME'] 
          . $_SERVER['REQUEST_URI'] 
          ; 
  $vEnc   = urlencode ($url) ;

# FLOAT RIGHT
  $vCss   = '<a href="'
          .   'https://jigsaw.w3.org/css-validator/validator?uri='
          .     $vEnc
          .   '&profile=css3svg&usermedium=all&warning=1&vextwarning=&lang=en"'
          . '>CSS: Validator'
          . '</a>'
          ;

# FLOAT LEFT
  $vHtml  = 'https://validator.w3.org/nu/?doc=' .$vEnc ;
  $vHtml  = '<a href="' .$vHtml .'"> HTML: Validator </a>' ;
  

 /* style.css 
  .bot {border: solid 1px #ccc;}
  .fll {float: left;} 
  .flr {float: right;}
  .fss {font-size: small;} 
  .ftr {position: fixed; left:0; bottom:0;} 
  .tac {text-align: center;}
  .w99 {width: 100%;}
*/

// PHP STRINGS HEREDOC Syntax
  echo $ftr = <<< ____EOT
    <p> <br> </p>

    <div class="ftr tac w99 fss">
      <b class="fll"> $vHtml </b>
      <b class="flr"> $vCss  </b>

      Wonderful place for a footer
    </div>  
____EOT;