Code style

Which code sample shows the proper use of indents and spaces?

A)

.header {
  background: white;
  border: 5px solid black;
  color: red;
  text-decoration: underline;
  text-align: left;
  margin: 0 0 1em 0;
}

B)

@keyframes appear{
  from{
    opacity: 0;
  } 
  to{
    opacity:0.8;
  }
}

C)

.menu {
  height: 100vh;
    width: 100%;
      padding: 1em 0 0 0;
        background: white;
          z-index: -1;
}

D)

.portfolio-item{
width: 16.6vw;
height: 16.6vw;
z-index: 1;
opacity: 0;
}