The ability to set the opacity on a colour differs subtly from setting the opacity on an element using the CSS opacity property. Here we have an H1 with foreground and background colours set against a page with a patterned background. Heading with no transparency applied. By setting the CSS opacity property, we can adjust the transparency of the entire element and its contents:.
RGBA colour gives us something different — the ability to control the opacity of the individual colours rather than the entire element. So we can set the opacity on just the background:. Just like rgb the first three values are red, green and blue. The fourth value is the opacity level from 0 completely transparent to 1 completely opaque. Fortunately, due to the robust design of CSS as a language, we can specify RGBA colours for browsers that support it and an alternative for browsers that do not.
The CSS parsing rules specify that any unrecognised value should be ignored. We can make use of this because a browser without RGBA support will treat a colour value specified with rgba as unrecognised and discard it.
So if we specify the colour first using rgb for all browsers, we can then overwrite it with an rgba colour for browsers that understand RGBA. Using the same principal as before, we can specify the background in a style that all browsers will understand, and then overwrite it in a way that browsers without RGBA support will ignore.
Imagine if you wanted to produce a pure blue color. But what if instead of blue you wanted fuchsia? From basic color theory, we know that the absence of any color results in black. In the following example, hexadecimal color notation was used. All major browsers support RGBA color notation. To put it in perspective, the CSS rgba notation has been around since Internet Explorer 9 which was launched in 3 years ago.
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Does this mean that the alpha value is actually used to change the colour in some sort of specific way? So, technically it's the same color with different transparency, but the perceived result will be a different color unless by chance the element behind the transparent one has the same color.
When you overlay it on a colored background, it can result in a different apparent color. The last value there is the opacity opposite of transparency measured from 0 to 1.
The first three values are just like a regular rgb CSS property. By setting an RGBA color value. You are really just setting the color and a separate opacity value.
This could be accomplished by setting the color with RGB and then the opacity separately with opacity, but RGBA combines the two into a single function. So, your two examples are setting the same value for color, but applying two different levels of opacity to that color. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. How does transparency in rgba work?
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