Regression: Unable to change borderWidth when border contains a CSS variable

[noahnu]

Reproducible test case:

it("should allow changing a single property on a border, when border contains a css variable", () => {
  const style = new CSSStyleDeclaration();
  style.border = "0.1rem solid var(--my-color-value)";
  style.borderWidth = "0.2rem";
  assert.strictEqual(style.borderWidth, "0.2rem");
  assert.strictEqual(style.border, "0.2rem solid var(--my-color-value)");
});

It fails on the style.borderWidth = "0.2rem"; line with:

TypeError [Error]: Cannot create property 'border-width' on string '0.1rem solid var(--my-color-value)'

This doesn't crash in cssstyle@v4.6.0 (though technically the individual property didn't change either, but at least it didn't crash).

[asamuzaK]

Confirmed crash.

But I think border shorthand should be empty then.

assert.strictEqual(style.border, "0.2rem solid var(--my-color-value)");

should be:

assert.strictEqual(style.border, "");