container above image collage in html (css)

Question

I have created a image collage and small sign in container.Now I want the container to be placed over images collage.

html

<section id="signin">
  <div class="photos">
        <img src="http://www.hdwallpapersimages.com/winter-tiger-wild-cat-images/31073/">
        <img src="http://www.hdwallpapersimages.com/winter-tiger-wild-cat-images/31073/">
        <img src = "http://www.hdwallpapersimages.com/winter-tiger-wild-cat-images/31073/">
        <img src = "http://www.hdwallpapersimages.com/winter-tiger-wild-cat-images/31073/">
        <img src="http://www.hdwallpapersimages.com/winter-tiger-wild-cat-images/31073/">
        <img src="http://www.hdwallpapersimages.com/winter-tiger-wild-cat-images/31073/">
  </div>
  <div class="sign container-fluid">
    <div class ="container">
      <div class="row section_blurb">
        <h1> Sign In </h1>
         <div class="col-xs-12 col-sm-4">
            <a href = "http://www.facebook.com">
            <img  src="images/ic_facebook blue.svg" class = "img-responsive" align = "left"><p>Sign in with facebook</p></a>
            <a href = "https://plus.google.com">
            <img  src="images/ic_google plus red.svg" class = "img-responsive" align = "left"><p>Sign in with google+</p></a>
            <a href = "https://instagram.com/">
            <img  src="images/ic_instagram blue.svg" class = "img-responsive" align = "left"><p>Sign in with instagram</p></a>
            <a href = "#email">
           <img   src="images/ic_email white.svg" class = "img-responsive" align = "left"><p>Sign in with Email</p></a>
        </div>   
      </div>     
    </div>
  </div>  
</section>

css

.photos {
   /* Prevent vertical gaps */
   line-height: 0;

   -webkit-column-count: 4;
   -webkit-column-gap:   0px;
   -moz-column-count:    4;
   -moz-column-gap:      20px;
   -moz-row-gap:         20px; 
   column-count:         4;
   column-gap:           0px;
   z-index: auto;


}

.photos img {
  /* Just in case there are inline attributes */
  width: 100% !important;
  height: auto !important;
  padding-bottom: 20px;
}

The container css is standard.There is also different section above and below signin section

Answer 1

You must place position:relative onto the parent:

#signin { position:relative; }

Then you can use absolute position, and items will be placed in relation to parent:

.photos { position:absolute; top:0; left:0; z-index:0; }
.sign { position:absolute; top:40px; right:40px; z-index:2; }

Here is article explaining: https://css-tricks.com/absolute-positioning-inside-relative-positioning/

Z-index can be trickier, but try simplest first. :)

Answer 2

I added the css for the ".container-fluid" class:

 .photos { /* Prevent vertical gaps */ line-height: 0; -webkit-column-count: 4; -webkit-column-gap: 0px; -moz-column-count: 4; -moz-column-gap: 20px; -moz-row-gap: 20px; column-count: 4; column-gap: 0px; z-index: auto; background:#adf; } .photos img { /* Just in case there are inline attributes */ width: 100% !important; height: auto !important; padding-bottom: 20px; } .container-fluid{ position:absolute; top:0; left:0; right:0; bottom:0; background:rgba(0,0,0,0.5); } 

 <section id="signin"> <div class="photos"> <img src="http://www.hdwallpapersimages.com/winter-tiger-wild-cat-images/31073/"> <img src="http://www.hdwallpapersimages.com/winter-tiger-wild-cat-images/31073/"> <img src = "http://www.hdwallpapersimages.com/winter-tiger-wild-cat-images/31073/"> <img src = "http://www.hdwallpapersimages.com/winter-tiger-wild-cat-images/31073/"> <img src="http://www.hdwallpapersimages.com/winter-tiger-wild-cat-images/31073/"> <img src="http://www.hdwallpapersimages.com/winter-tiger-wild-cat-images/31073/"> </div> <div class="sign container-fluid"> <div class ="container"> <div class="row section_blurb"> <h1> Sign In </h1> <div class="col-xs-12 col-sm-4"> <a href = "http://www.facebook.com"> <img src="images/ic_facebook blue.svg" class = "img-responsive" align = "left"><p>Sign in with facebook</p></a> <a href = "https://plus.google.com"> <img src="images/ic_google plus red.svg" class = "img-responsive" align = "left"><p>Sign in with google+</p></a> <a href = "https://instagram.com/"> <img src="images/ic_instagram blue.svg" class = "img-responsive" align = "left"><p>Sign in with instagram</p></a> <a href = "#email"> <img src="images/ic_email white.svg" class = "img-responsive" align = "left"><p>Sign in with Email</p></a> </div> </div> </div> </div> </section> 

now the "signin-container" is outside the ".photos div", because it is inside the #signin it has its dimensions. You can move your "signin-container" div inside the photos one and it will be perfectly overlapped.