Setting color via rgba in CSS

In addition to the rgb format, there is the rgba format, which works in a similar way, but the fourth parameter allows you to set the translucency of the color. This parameter accepts fractional values from 0 to 1. In this case, one corresponds to full opacity, and zero to full transparency.

Let's look at some examples.

Example

First, let's make an opaque block like this:

<div id="parent">
	<div id="elem">
		Lorem ipsum dolor sit amet.
	</div>
</div>

#parent {
	background-image: url("bg.png");
	background-repeat: no-repeat;
	background-size: cover;
	display: inline-block;
	padding: 30px;
}
#elem {
	width: 300px;
	height: 200px;
	border: 20px solid red;
	padding: 10px;
	font-size: 50px;
	font-weight: bold;
	color: rgba(255, 0, 0); /* red gules */
}

Example

Now let's add translucency to the text:

<div id="parent">
	<div id="elem">
		Lorem ipsum dolor sit amet.
	</div>
</div>

#parent {
	background-image: url("bg.png");
	background-repeat: no-repeat;
	background-size: cover;
	display: inline-block;
	padding: 30px;
}
#elem {
	width: 300px;
	height: 200px;
	border: 20px solid red;
	padding: 10px;
	font-size: 50px;
	font-weight: bold;
	color: rgba(255, 0, 0, 0.5); /* red translucent */
}

Example

Now let's make a translucent border:

<div id="parent">
	<div id="elem">
		Lorem ipsum dolor sit amet.
	</div>
</div>

#parent {
	background-image: url("bg.png");
	background-repeat: no-repeat;
	background-size: cover;
	display: inline-block;
	padding: 30px;
}
#elem {
	width: 300px;
	height: 200px;
	border: 20px solid rgba(255, 0, 0, 0.5); /* red translucent */
	padding: 10px;
	font-size: 50px;
	font-weight: bold;
	color: red;
}

Example

Now let's make a semi-transparent background:

<div id="parent">
	<div id="elem">
		Lorem ipsum dolor sit amet.
	</div>
</div>

#parent {
	background-image: url("bg.png");
	background-repeat: no-repeat;
	background-size: cover;
	display: inline-block;
	padding: 30px;
}
#elem {
	width: 300px;
	height: 200px;
	border: 20px solid red;
	background-color: rgba(0, 0, 0, 0.4); /* black translucent */
	padding: 10px;
	font-size: 50px;
	font-weight: bold;
	color: red;
}

Practical tasks

Set the paragraphs to a red translucent color.

Set the background color to green and semi-transparent.

Set the border color to blue and semi-transparent.