HTML and CSS Reference
In-Depth Information
Miranda's Acronym Cheat Sheet
WE techies love our acronyms. Let me
explain the common ones in this chapter:
RGB , RGBA , HSL , and HSLA . The seven letters
mean the same thing in all four.
R = Red
Hue = H
G = Green
B = Blue
Saturation = S
Luminosity = L
A =
Alpha (Opacity)
= A
Sometimes you don't want to make an
entire element transparent or semi-
transparent. If you refer back to the
example from listing ch09/opacity-
4.html, the text and the background
are semitransparent.
If you want people be able to read large amounts of text like this, then
a semitransparent background would be better combined with fully
opaque text. Rather than make the entire element semitransparent,
CSS3 provides several ways of specifying color values that have a level
of transparency, the first of which is rgba() . You can use rgba() to make
just the background transparent. If you're used to the hexadecimal
shorthand for specifying colors, these two diagrams show how they're
Blue component
red component
Green component
red component
background: #666666;
opacity: 0.5;
background: rgba(102, 102, 102, 0.5);
Blue component
Green component
Alpha Transparency
50% opacity element with a
dark gray background
Element with a background that is
both dark gray and 50% opacity
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