Can't pass variable from theme hook or controller to custom template
You cannot use #markup and #theme in the same element. #markup will always take precedence, and #theme is ignored. If you want to output some markup, you need to include that as part of your theme. If the markup is dynamic, then include it as a variable to be passed to your theme (though you need to name the variable as something other than markup).

You've also defined the variable as toto in your hook_theme() implementation, then passed the value in #tutu in your render array. You need to use '#toto' =&gt; 'some value'.