How to fix a footer overlapping content?

Question 1

Change this:

#footer {
    bottom: 0;
    color: #707070;
    height: 2em;
    left: 0;
    position: relative; //changed to relative from fixed also works if position is not there
    font-size: small;
    width:100%;
}

Demo

Question 2

Anyone stumbling upon this in 2017 should know that a great option was invented to alleviate layout headaches such as this, flexbox.

Essentially, all you have to do is set <body> to:

body {
  display: flex;
  flex-direction: column;
  align-items: center;
}

Then apply flex:1 1 auto to the "main" or middle section, in this case #container, which will make it expand vertically to fill available space, assuring the footer will stick to the bottom:

#container {
      flex: 1 1 auto;  /*grow vertically*/
}

We added align-items:center in the flex parent to handle cross-axis centering (in our case, horizontal).

Here is an example snippet of the above:

html,
body {
  margin: 0;
  padding: 0;
}

body {
  font-family: Arial, Helvetica, sans-serif;
  background: #252525;
  border-left: 1px solid #111;
  border-right: 1px solid #111;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  align-items: center;
}

#container {
  color: white;
  background: #363636;
  padding: 2em;
  background: #363636;
  flex: 1 1 auto;
  /*grow vertically*/
  width: 55%;
  text-align: center;
}

#footer {
  color: #707070;
  height: 2em;
  font-size: small;
}

<body>
  <div id="container">
    <h1>A webpage</h1>

    <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nullam pretium augue quis augue ornare tempor. Donec eu purus vitae nisi eleifend euismod. Nullam sem nunc, bibendum tempor iaculis eu, consequat in sem. Phasellus nec molestie orci. Fusce varius
      nisi est, non aliquet dolor porttitor non. Aliquam eu ante nec massa pulvinar posuere. Praesent consectetur porttitor ipsum, eget viverra urna ultricies et.</p>
    <p>Quisque vehicula neque a enim dignissim, et vestibulum orci viverra. Pellentesque aliquam feugiat interdum. Ut molestie vitae lacus in eleifend. Sed scelerisque urna ut elit venenatis suscipit. Nullam nec urna vel enim mattis interdum ut consequat
      libero. Proin in imperdiet orci. Vivamus felis lacus, dictum ac eros eu, malesuada pretium nisi. Cras suscipit nunc magna, a egestas neque facilisis sed.</p>
  </div>
  <div id="footer">This is a footer.</div>
</body>

Question 3

See DEMO

I have made some CSS changes. Have a look. I hope it will help you.

Updated CSS

#footer {
 bottom: 0;
 color: #707070;
 height: 2em;
 left: 0;
 position: fixed; /* OldProperty */
 position: static;/* Updated Property */
 font-size: small;
 width:100%;
}

Question 4

I believe you were looking for a sticky footer that stays while not being fixed to the bottom of the page (so no overlap).

Solution

The solution comes from Chris Bracco and I am going to detail what you need to reproduce the effect:

HTML

Your HTML be like:

<html>

<body class="body-for-sticky">
    <...> your content </...>
    <div class="footer sticky-footer"> your footer </div>
</body>

</html>

CSS

You will need to add in your css something like:

html {
    height: 100%;              /* for the page to take full window height */
    box-sizing: border-box;    /* to have the footer displayed at the bottom of the page without scrolling */
}

*,
*:before,
*:after {
    box-sizing: inherit;       /* enable the "border-box effect" everywhere */
}

.body-for-sticky {
    position: relative;        /* for the footer to move with the page size */
    min-height: 100%;          /* for the footer to be at the bottom */
    padding-bottom: 6rem;      /* Space available between last element and bottom border of the page */
}

.sticky-footer {
    position: absolute;        /* for it to disappear under last body element */
    bottom: 0;                 /* so the footer can stick to the bottom*/
}

Example

That's like the basic you need to create the sticky footer. Here is an example (with some more CSS for better rendering).

html {
      height: 100%;
      box-sizing: border-box;
    }
    
    *,
    *:before,
    *:after {
      box-sizing: inherit;
    }
    
    .body-for-sticky {
      position: relative;
      min-height: 100%;
      padding-bottom: 6rem;
    }
    
    .sticky-footer {
      position: absolute;
      bottom: 0;
    }
    
/* for the rendering */

    body {
      margin: 0;
      font-family: "Helvetica Neue", Arial, sans-serif;
    }
    
    .footer {
      right: 0;
      left: 0;
      padding: 1rem;
      background-color: #efefef;
      text-align: center;
    }
    
    .demo {
      margin: 0 auto;
      padding-top: 64px;
      max-width: 640px;
      width: 94%;
    }

<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="utf-8">
  <title>Sticky footer</title>
    <style>  </style>
</head>

<body class="body-for-sticky">

  <div class="demo">
    <h1 style="margin-top: 0">CSS “Always on the bottom” Footer</h1>

    <p>I often find myself designing a website where the footer must rest at the bottom of the page, even if the content above it is too short to push it to the bottom of the viewport naturally.</p>

    <p>However, if the content is taller than the user’s viewport, then the footer should disappear from view as it would normally, resting at the bottom of the page (not fixed to the viewport).</p>

    <p>If you know the height of the footer, then you should set it explicitly, and set the bottom padding of the footer’s parent element to be the same value (or larger if you want some spacing).</p>

    <p>This is to prevent the footer from overlapping the content above it, since it is being removed from the document flow with <code>position: absolute;</code>.</p>

    <p> Source <a href="https://chrisbracco.com/css-sticky-footer-effect" />Chris Bracco</a>.</p>
  </div>

  <div class="footer sticky-footer">This footer will always be positioned at the bottom of the page, but <strong>not fixed</strong>.</div>

</body>

</html>

Expand the snippet and watch the result full size to see how it works.

Question 5

First write this code

footer {
background-color: #000;
color: #FFFFFF;
font-size:.8em;
margin-top:25px;
padding-top: 15px;
padding-bottom: 10px;
position:fixed;
left:0;
bottom:0;
width:100%;
}

and now set media queries

@media only screen and (max-width: 767px){
    footer {
      background-color: #000;
      color: #FFFFFF;
      font-size:.8em;
      margin-top:25px;
      padding-top: 15px;
      padding-bottom: 10px;
      position:static;
      left:0;
      bottom:0;
      width:100%;
    }
}

hope this will help you :)

Question 6

 #footer {
     z-index: 1;
     position: absolute;
     right: 0;
     bottom: 0;
     left: -25%;
     padding: 1rem;
     background-color: black;
     text-align: center;
     height: 3em;
     left: 0;
     font-size: small;
     width:100%;
 }