Navigation bar display mixed previous one when navigating + button half visible

I have my navigation bar titles stacking like apparently a lot of people. I tried the code provided by tuanphan (cf below) and it worked fine but when I navigate I see the previous display before it returns to the new one. The second issue is that the "Work with me" button is so pushed on the right side that it is hidden. Can anyone help to change the position of the button to be completely visible? 

my url is  https://bullfrog-collie-jwf9.squarespace.com/config/design

/* nav one line */
.header-title-nav-wrapper {
    flex: 0 0 90% !important;
}

Hi. What is your site url? We can check easier