Why do backgrounds disappear when opening normal html on the site?

Question

HTML

I write code through prepros and if you open the layout through it, then everything is in order. If you just open index.html in the browser, all the pictures that are set by the photon do not work. Tell me what's wrong.
.wrapper {
margin: 0 auto;
background: url("../../img/bg_1section.png") 0 0/100% 100% no-repeat;
}