New lint rule: disallow non-token values

[bennypowers]

Proposed new rule would disallow non var(--rh-*) values for certain properties, among them:

• color
• background-color
• font-size
• font-weight
• font-family
• box-shadow

Why?

The purpose of this rule is to enforce brand standards and catch design errors sooner. In cases where a non-token value is genuinely and legitimately desired, a lint ignore comment would be required, and a reason provided in situ.

❌ The following CSS would ERROR under this rule:

font-weight: 300;
color: blue;
font-family: RedHatText, Overpass, sans-serif;
padding: 0 32px;

✔️ The following CSS would be ALLOWED under this rule:

font-weight: var(--rh-font-weight-body-text-regular);
font-family: var(--rh-font-family-body-text);
color: var(--rh-color-blue-500);
padding: 0 var(--rh-space-xl);

Note that 0 is allowed for padding;