We often declare variables using the :root selector that targets the html element. We can then access these variables using the var() function.

:root {
  --color-primary: #ffdd36;
  --border-size: 2px;
  --border-radius: 10px;
}

.one {
  background: var(--color-primary);
}

.two {
  background: var(--color-primary);
}