[Theme: Simply read] Active menu item on selected post

Hi,

I am trying for quite a long time to solve this mistery. I am creating website https://www.srilankaprzedownik.pl and I use links, not pages in main menu. E.g. when you click menu item “KONTAKT”, you will go to post (not page) that I prepared. I really need links in menu to be posts, not pages. Everything works fine, except different apperance for active menu. I would like to change a color of menu item of current post like it is on home page (STRONA GLOWNA). Belive me or not – I have tried all postid-xxx #menu-item-xxx configurations and it doesn’t work. I inspected elements, copied all the classes, id’s and really tried everything that came up to my mind. And it just doesn’t work. I only managed to have “SRI LANKA” menu item color changed, but on all pages/posts. The code is:

#menu-item-154 a  {
    color: #197F20 !important;}

But no class can make it appear only on specified post. What is more when I want to set different featured images for different posts in custom css, .postid-xxx works like a charm. It only has problem with changing menu items.

PLEASE HELP ??