How to put something after the header but before the content

may I please ask for your help?
I need to put an adsende code after title of a post and befor eteh content of apost, but I do not want to copy the code each tiem in the single post, but do something automatic.
in other themes i usually copy teh code in the “single” .css in the theme editor, but in this theme i do not know how to modify the single.css
Mnay thanks

If you will modify single.php template then you will have to replace this code each time new theme update comes out. To avoid this you can use plugins such as Quick Adsense or even official Google Adsense plugin for WordPress.