Convert htaccess to nginx rewrite rule

I want to convert this to nginx rules

# BEGIN EAP Rewrite
<IfModule mod_rewrite.c>
RewriteEngine on
Options -Multiviews
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^(.*)?$ index.php?a=$1	[QSA,NC,L]
ErrorDocument 404 /new/404.php
</IfModule>
# END EAP Rewrite

I have tried several, but no luck.

error_page 404 /new/404.php;
	location / {
		#try_files $uri $uri/ /index.php?$args;
		try_files $uri $uri/ /index.php?a=$args; 
		#rewrite  ^/(.*)?$  /index.php?a=$1 last;
	}

Actually, this line below worked for the URL but real folder paths, like css and js, are not working.

#rewrite  ^/(.*)?$  /index.php?a=$1 last;

Anyone? thanks in advance.