CSS is not HTML. is a named character reference in HTML; equivalent to the decimal numeric character reference  . 160 is the decimal code point of the NO-BREAK SPACE character in Unicode (or UCS-2; see the HTML 4.01 Specification). The hexadecimal representation of that code point is U+00A0 (160 = 10 × 161 + 0 × 160). You will find that in the Unicode Code Charts and Character Database.
In CSS you need to use a Unicode escape sequence for such characters, which is based on the hexadecimal value of the code point of a character. So you need to write
.breadcrumbs a:before {
content: '\a0';
}
This works as long as the escape sequence comes last in a string value. If characters follow, there are two ways to avoid misinterpretation:
a) (mentioned by others) Use exactly six hexadecimal digits for the escape sequence:
.breadcrumbs a:before {
content: '\0000a0foo';
}
b) Add one white-space (e. g., space) character after the escape sequence:
.breadcrumbs a:before {
content: '\a0 foo';
}
(Since f is a hexadecimal digit, \a0f would otherwise mean GURMUKHI LETTER EE here, or ? if you have a suitable font.)
The delimiting white-space will be ignored, and this will be displayed foo, where the displayed space here would be a NO-BREAK SPACE character.
The white-space approach ('\a0 foo') has the following advantages over the six-digit approach ('\0000a0foo'):
Thus, to display a space after an escaped character, use two spaces in the stylesheet –
.breadcrumbs a:before {
content: '\a0 foo';
}
– or make it explicit:
.breadcrumbs a:before {
content: '\a0\20 foo';
}
See CSS 2.1, section "4.1.3 Characters and case" for details.