RegExpr with lookahead and lookbehind

[Admin_LB]

I've tested the following expression successfully with the regExCoach:
(?<=<span>)[0-9.]*(?=</span>) for the following tagetstring <span>123.45</span> to extract the number.

But the test in the zabbix regex editor fails:



Do I have a mistake with my thinking?
Is there any way to extract values like this from a website?

Many thanks!

[albert_ra]

I've tried negative lookahead with logrt, and it workd.