RewriteEngine On

RewriteBase /

# category17.html?offset=30 -> index.php?categoryID=17&offset=30
RewriteRule ^category([0-9]+).html?offset=([0-9]+)$ index.php?categoryID=$1%&offset=%2  [L]
^^^^^ не работает ^^^^^

# category17.html -> index.php?categoryID=17
RewriteRule ^category(.+).html$ index.php?categoryID=$1 [L]

strip per-dir prefix: /home/xxx/domains/xxx/public_html/category17.html -> category17.html
applying pattern '^category([0-9]+).html?offset=([0-9]+)$' to uri 'category17.html'
strip per-dir prefix: /home/xxx/domains/xxx/public_html/category17.html -> category17.html
applying pattern '^category(.+).html$' to uri 'category17.html'
rewrite 'category17.html' -> 'index.php?categoryID=17'
split uri=index.php?categoryID=17 -> uri=index.php, args=categoryID=17