Darken image overlay and add text over it in CSS

Question

How would I darken (add a semi-transparent overlay) and add text to this image (but centred horizontally and vertically) as below:

HTML

<img src="http://luxurylaunches.com/wp-content/uploads/2014/05/uber-london.jpg" id="top" data-appear-animation="fadeIn">

CSS

#top {
  width: 100%;
  height: auto;
}
body {
  margin: 0px;
}

Fiddle here: http://jsfiddle.net/6jf0nxd5/

Answer 1

To center the text horizontaly and verticaly, you will need to wrap it in a container with text-align:center;. Then you can use a pseudo element to center it verticaly. For the overlay, you can give the text container a rgba() background color that can have transparency :

DEMO

body {
    margin: 0px;
}
.wrap{
    position:relative;
}
.wrap img{
    width:100%;
    height:auto;
    display:block;
}
.text{
    position:absolute;
    top:0; left:0;
    width:100%; height:100%;
    background:rgba(255,255,255,.5);
    text-align:center;
}
.text:after{
    content:'';
    width:1px; height:100%;
    vertical-align:middle;
    display:inline-block;
}
.text span{
    display:inline-block;
    vertical-align:middle;
}

<div class="wrap">
    <img src="http://luxurylaunches.com/wp-content/uploads/2014/05/uber-london.jpg" id="top" data-appear-animation="fadeIn" />
    <div class="text"><span>Text over the image
        <br/>Second line</span></div>
</div>