How to find a CSS value and replace it in CSS file

Hi all,

In one of my project I deleted the "autoPlayButton" and I've uploaded a picture that I designed with the same color as the backgroud color of the project, but, when I launch the project It seems that there is an element above this picture, which change the color, I tried with to inspect the code, I've found this div, when I set the background-color to transparent, this element disapear which what I want, but when I go to the CSS file of the project, I find the class "cp-movie" but without the value of the background-color, and I don't knwo where I can find it to be able to edit it.

<div id="project" class="cp-movie" style="width: 1920px; height: 1080px; background-color: rgb(255, 255, 255); left: 0px; top: 0px; z-index: 1; display: block;">

Thank you for your help.

Karim