AP Mega Menu in Astra set transparent

Hello,

I use Astra for my website, want to add mega menu (found AP mega menu free version).
I need that menu buttons would be white or transparent.

Found in available skins that there is “Clean white” – thought “cool”, but after I set it, color of button is white, but border still in color (frame left) – I dont need.

This menu has “custom CSS” field, I tried to enter there:

.navigation-top {
    background: transparent;
    border: 0;
}

It does not work. Tried to change the name .towpmega-menu-primary { – no luck.

What I made wrong?

How to fix the menu be without borders, or you know good mega menu for free with lot of settings which I can use?