How do you write htaccess rules? Please, in? Fill in the contents of the number. Thank you (urgent)

How do you write htaccess rules? Please, in? Fill in the contents of the number. Thank you (quick and urgent)
The original
index.php?id=123 Conversion
123.html

Htaccess as follows:

Rewriteengine on
Rewriterule ^ ([0-9]+). html$? id=$1


I'm trying to get the original 123 encrypted. With this base64_encode.

Index.php?id=mtiz
Mtiz.html

How do you write htaccess rules?

Rewriteengine on
??????????????????????????????????


------Solution--------------------
Rewriterule ^ (. +). html$? id=$1

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