HTML and CSS Reference
In-Depth Information
RGBa Color
This is like RBG color but adds an alpha
channel value to specify the opacity of the
color. An RGBa is specified via a function
style rgba( r , g , b , a ) value, where colors
r, g, and b are specified as a decimal
value from 0 to 255 or a percentage from
0 to 100%, and the alpha channel value
for defining opacity is a number between
0 (fully transparent) and 1 (fully opaque).
Values outside this range will be rounded
up or down to fit the closest value.
#redtrans {
There are numerous keyword values found
in CSS for specifying sizes ( xx-large ),
border styles ( dashed ), text-formatting
( underlined ), element meaning ( block ),
layout ( absolute ), and more. If a value
is not found within quotes or followed
by a measurement, it is likely a keyword
or counter. If it isn't or is simply not an
understood value, it will be ignored by CSS-
conforming user agents.
.big {
font-size: xx-large;}
#box {
border: 1px solid black;}
#boom {
border: 3px crazy black;}
/* value of crazy
is ignored */
ol.cT {
list-style-type: none;}
ol.cT li:before {
counter(counter1) " - " ;}
There are occasions where CSS supports
simple positive or negative integer values
like 2 and -3 as well as real numbers like
3.5. Note that in the case of 0 values, it
is not required to put a measurement unit
like px and thus a plain zero value will be
commonly seen.
p {line-height: 2;}
/* same as 200% */
* {margin: 0;}
Percentages are denoted by a number
followed by the % symbol and are always
relative to another value such as a length.
Quite often they are used to specify some
value relative to an inherited value from a
parent element.
body {font-size: 10px;}
body > p.big
{font-size: 200%;}
/* 20 px */
body > p.small
{font-size: 50%;}
/* 5px */
T ABLE 4-11 CSS Units and Lengths
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