This is my second answer, I created this instead of adding it to my initial answer because the method is different.
In your HTML (index) file, add the image like this:
<img id="imgBackground" src="http://we-fly.ddns.net/images/back.jpg" />
(I suggest adding it directly after the body tag)
In your CSS, I am just going to post the entire thing, Its a little funny because your last @Media (Min-Width: 601px) is overriding your default for your desktop page... you may want to consider deleting this Media Query... See comments in code below to see changes:
/* Set initial values for your image background */
#imgBackground{
position:absolute; /* Absolute Positioning so we can use "top" and "Left" */
top:0px; /* Set top edge to 0px (Top of the screen) */
left:0px; /* Set left edge of image to 0px, so it starts at the left edge of the screen. */
width:100%; /* We want our widt to be 100% of our browser window */
height:auto; /* we don't care about the image height, so let it set itself based on the image's proportions */
position:fixed; /* Make our image scroll with the user so if they can scroll they don't leave our background behind, exposing the white "body" tag background. */
}
body {
text-align: center;
background-position: center center;
background-repeat: no-repeat;
background-attachment: fixed;
background-size: cover;
margin: 0;
padding: 0;
}
#quote-conatiner {
position: fixed;
margin: auto auto 24px auto;
bottom: 20%;
left: 0;
right: 0;
text-align: center;
background-color:rgba(180, 180, 180, .4);
}
h3 {
font-family: Garamond sans-serif;
color: white;
width: 80%;
margin: .5em auto .5em auto;
}
.button {
font-family: sans-serif;
text-decoration: none;
padding: .3em 0.6em;
border-radius: 8px;
border: 2px solid #59169c;
background-color: #417;
color: white;
box-shadow: 0 0 64px black;
}
.button-container {
position: fixed;
margin-left: auto;
margin-right: auto;
top: 80%;
left: 0;
right: 0;
}
.button:active {
background-color: #330855;
}
@media only screen and (max-width: 600px) {
/* set image background to achieve max Height and we don't care about width (auto) on mobile displays. */
#imgBackground{
position:absolute;
top:0px;
left:0px;
width:auto;
height:100%;
position:fixed;
}
body {
margin: 0;
padding: 0;
}
h3 {
font-size: 1.2em;
}
.button {
font-size: 1.4em;
}
}
@media only screen and (max-width: 400px) {
/* set image background to achieve max Height and we don't care about width (auto) on mobile displays. */
#imgBackground{
position:absolute;
top:0px;
left:0px;
width:auto;
height:100%;
position:fixed;
}
body {
margin: 0;
padding: 0;
}
h3 {
font-size: 0.8em;
}
.button {
font-size: 1.0em;
}
}
/* May want to consider getting rid of this Query, if you don't it is overriding your styles set above your media querys. */
@media only screen and (min-width: 601px) {
/* Set image background qualities for any display larger than 601px.*/
#imgBackground{
position:absolute;
top:0px;
left:0px;
width:100%;
height:auto;
position:fixed;
}
body {
margin: 0;
padding: 0;
}
h3 {
max-width: 600px;
font-size: 1.3em;
}
.button {
font-size: 1.3em;
}
}