Answers for "how to get the full image in background on css"

make background image full width

html {
    height: 100%;
}
body {
    color: #999;
    background: url('../images/background/main_bg.jpg') no-repeat center center fixed;
    font-family: 'Roboto', sans-serif;
    -webkit-background-size: cover;
    -moz-background-size: cover;
    -o-background-size: cover;
    background-size: cover;
}

how to cover full background with css

<div id="bg">
  <img src="images/bg.jpg" alt="">
</div>