Adding image above portfolio filter

Hello,

I’m trying to add an image above each portfolio filter heading. I’ve managed to do it when i work in firebug but when i add the code to the custom css of my theme it’s not working because the ID is changing on refresh:

#fws_55d0d78289570 > div:nth-child(2) > div:nth-child(1) > div:nth-child(1) > div:nth-child(1) > div:nth-child(1) > ul:nth-child(2) > li:nth-child(5) > a:nth-child(1)  {
    background-image: url("https://perida.nl/wp/wp-content/uploads/2015/08/eetkamer.jpg");
    background-position: center top;
    margin-top: 10px;
    padding: 140px 70px 20px 70px;
    background-repeat: no-repeat;
    display: block;
    -webkit-box-shadow: 0px 0px 10px 0px rgba(0,0,0,0.75);
    -moz-box-shadow: 0px 0px 10px 0px rgba(0,0,0,0.75);
    box-shadow: 0px 0px 10px 0px rgba(0,0,0,0.75);
    border-radius: 25px;
    background-size: 150px !important;
    font-size: 2em;
}

for the website: https://www.perida.nl/wp/
the portfolio is below the slider.

Hope someone can help, much appriciated!

Regards,
Rein