no only though site collection. Get your site collection admin to apply the change.
He/She might say no. With sp online once you make the change to have publishing feature active there is no going back even if you disable it.
good luck ;)
so the question is: is it possible to apply css without the publishing feature?
if its on a modern site yes as the publishing feature is not available and would need to be done some other way like spfx extension.
for a classic site without publishing feature enabled means its pretty much a team site. If you dont have site collection level admin access then very little chance of having powershell access to make changes. Changing the master page is a no no as its a living document (constantly updated by ms) so would find yourself constantly updating the master page to keep up with the changes.
option 2 would be to activate at site collection level and then create a sub site as a publishing site or activate the feature on an existing site.
as noted this could be a bit of a hard sell depending on requirements and if the admin is willing as it effects other areas. my personal option is that they should and think most do for the benefits it brings.
this option requires site collection admin or site owner to activate the publishing feature at the site collection level and then you can activate a the sub site level
option 3 leave the site collection level alone (parent). If possible create a new sub site under the site collection site that is a team site (classic). when selecting the template click on publishing -> select publishing site.
this would create a sub site that is a publishing site under a team site:
team site (site collection) parent level -> publishing site (sub
this is ok as it doesnt change the parent level, only issue is inconstancy because you have the option to change the css and master page in sub site and all its sub sites.
this option does not require site collection admin or site owner to activate the publishing feature at the site collection level but might require them to create a publishing subsite.
When i create anything i would create a team site and activate the publishing feature for the site collection. Reason behind this is to manipulate the css and have a consistent global branding though all sub sites and to have all the functionality of the team site as a publishing site with css and mastpage. from this point all subsites inherit the publishing feature (active) and inherit the branding.