View width not 100% on iPhone X in landscape mode

To test this issue I just added a coloured section with 100% width. When I open up this site on my iPhone X it shows white space left and right. Why does this happen?

I found a similar topic:

This solved my problem at first glance.

Any idea how to add the safe-area-inset?

padding: env(safe-area-inset-top) env(safe-area-inset-right) env(safe-area-inset-bottom) env(safe-area-inset-left);

How and where exactly do I have to add this code to apply it globally? In the projects settings custom / footer code, right? I tried but couldn’t make it work.

My current website: