Base64 is encoded differently in bash and in online services, what's the point?

Question

bash

For example, if the text "1.txt" is encoded using base64.ru, then the result will be:
MS50eHQ=

If you use bash in debian or macos, then the output is slightly different:
$ echo 1.txt | base64
MS50eHQK
Why? How to fix output in bash?)

Answer 1

echo -n 1.txt | base64
-n means don't add a newline at the end