This example includes four hot pink squares, with fully opaque or semi-transparent backgrounds created using four different-length case-insensitive hex-color syntaxes.
HTML
<div>
#F09
<div class="c1"></div>
</div>
<div>
#f09a
<div class="c2"></div>
</div>
<div>
#ff0099
<div class="c3"></div>
</div>
<div>
#FF0099AA
<div class="c4"></div>
</div>
CSS
The hot pink background colors are created using the three-, four-, six-, and eight-value hex notations, using both uppercase and lowercase letters.
[class] {
width: 40px;
height: 40px;
}
.c1 {
background: #f09;
}
.c2 {
background: #f09a;
}
.c3 {
background: #ff0099;
}
.c4 {
background: #ff0099aa;
}
Result