Hi Caglar,
My colleague is correctly said that you need to set the Mix Blend attribute value to multiply, darken, difference, or normal. I would suggest you modify the custom CSS code in the Element CSS of the specific Bar and add the following.
mix-blend-mode: multiply;
The code should look like:
.$el.x-bar {
height: 6em;
font-size: 20px;
background-color: rgb(0,0,0);
z-index: 9999;
mix-blend-mode: multiply;
-webkit-backdrop-filter: invert(100%);
backdrop-filter: invert(100%);
transition-timing-function: cubic-bezier(0.400,0.000,0.200,1.000);
}


Hope it helps.
Thanks