Sibling Element ↔ Elements at same level

References

1. Adjacent Sibling Selector ↔ + Selector for Sibling Element; E1 + E2 {} where E2 is selector target

2. select <p\> which are [**_Sibling Element_**](sibling-element) of <h1\> ↔

h1 + p {
  font-size: 18px;
}