The easiest way to set transparent background color to a HTML element, without affecting the text-content is to use the rgba() function in CSS.
- The rgba() function is supported by all major browsers (IE 9+).
Example:
<style type="text/css">
#dv1 {
  position: relative;
  width: 78%;
  height: 8em;
  background: rgb(128, 139, 210);     /* For browsers that don't support rgba */
  background-color: rgba(128, 139, 210, 0.5);   /* Transparent background color */
}
</style>

<div id="dv1">
Semi-transparent background color, not affecting text content.<br/>
CSS code snippets from: <a href="http://coursesweb.net/" title="CSS Course">http://coursesweb.net/css/</a>
</div>
Result:
Semi-transparent background color, not affecting text content.
CSS code snippets from: http://coursesweb.net/css/

Transparent Background Image

To create a transparent background image with CSS, the trick is to insert a pseudo element with a image for background and regular opacity, the exact size of the element behind it.
- The pseudo elements are supported by all major browsers (IE 8+).
Example:
<style type="text/css">
#dv2 {
  position: relative;
  width: 78%;
  height: 8em;
  background-color: #fefe90;
  font-size: 1.3em;
}
#dv2::before {
  position: absolute;
  top: 0;
  left: 0;
  bottom: 0;
  right: 0;
  margin: 0;
  content: "";
  background: url('image.jpg');
  background-repeat: no-repeat;
  background-position: 30% 50%;
  opacity: 0.5;
}

/* Settingas for mouse over the element */
#dv2:hover::before {
  position: absolute;
  top: 0;
  left: 0;
  bottom: 0;
  right: 0;
  margin: 0;
  content: "";
  background: url('image.jpg');
  background-repeat: no-repeat;
  background-position: 30% 50%;
  opacity: 0.7;
}
</style>

<div id="dv1">
Semi-transparent background color.<br/>
CSS code snippets from: <a href="http://coursesweb.net/" title="CSS Course">http://coursesweb.net/css/</a>
</div>
Result:
Semi-transparent background image.
CSS code snippets from: http://coursesweb.net/css/

Daily Test with Code Example

HTML
CSS
JavaScript
PHP-MySQL
Which tag adds a new line into a paragraph?
<b> <br> <p>
First line ...<br>
Other line...
Which CSS property can be used to add space between letters?
text-size word-spacing letter-spacing
#id {
  letter-spacing: 2px;
}
What JavaScript function can be used to get access to HTML element with a specified ID?
getElementById() getElementsByTagName() createElement()
var elm = document.getElementById("theID");
var content = elm.innerHTML;
alert(content);
Click on the "echo" correct instruction.
echo "CoursesWeb.net" echo "CoursesWeb.net"; echo ""CoursesWeb.net";
echo "Address URL: http://CoursesWeb.net";
Transparent Background, but not the text-content on it

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