Generated by SassMeister.com.

input.scss

.header{
    margin: 1.5rem;
    background-color: green;
    display: flex;
    justify-content: space-between;
    
    &-nav{
        background-color: white;
        width: 60%;
        
        ul{
            list-style-type: none;
            
            li{
                display: inline-block;
            }
        }
    }
}

output.css

.header {
  margin: 1.5rem;
  background-color: green;
  display: flex;
  justify-content: space-between;
}
.header-nav {
  background-color: white;
  width: 60%;
}
.header-nav ul {
  list-style-type: none;
}
.header-nav ul li {
  display: inline-block;
}