how to set the footer at the bottom of the page code example

Example 1: why is my footer not at the bottom html

#footer {
   position:fixed;
   left:0px;
   bottom:0px;
   height:30px;
   width:100%;
   background:#999;
}

//name footer id="footer"

Example 2: how to set the footer at the bottom using css

#page-container {
  position: relative;
  min-height: 100vh;
}

#content-wrap {
  padding-bottom: 2.5rem;    /* Footer height */
}

#footer {
  position: absolute;
  bottom: 0;
  width: 100%;
  height: 2.5rem;            /* Footer height */
}

Example 3: keep footer at bottom of page

#footer {
  position: relative;
  margin-top: -180px;
  /* negative value of footer height */
  height: 180px;
  clear: both;
 /*Custom styling*/
}

/* Opera Fix thanks to Maleika (Kohoutec) */

body:before {
  content: "";
  height: 100%;
  float: left;
  width: 0;
  margin-top: -32767px;
  /* thank you Erik J - negate effect of float*/
}