I'm not sure what you mean by 'applying' it - any good editor should let you format your code however you like.
I had to look up what 'Allman style' was though, this particular style is very very uncommon in CSS files so you're unlikely to run into it in many existing CSS libraries and frameworks, or in tutorials.
Most CSS is formatted like this:
selector {
property: value;
property: value;
}
Even though it's valid to write it many many different ways:
selector{property:value;property:value}
selector
{
property
:
value
;
property
:
value
}
CSS has no concept of line breaks in the language, so where you're free to add any amount of whitespace you really are free to add it however you like it!