Why is this an issue?

To perform calculations when specifying a CSS property calc() function can be used. This function takes single expression as parameter. When writing this expression some rules must be respected:

• no empty calc()
• there should be an operator between the arguments
• there should not be any division by zero

Otherwise calc() function will be invalid and the entire rule using it will be ignored.

Noncompliant code example

.btn {
  border: solid black 1px;
  width: calc(100% 80px);  /* Noncompliant */
}

Compliant solution

.btn {
  border: solid black 1px;
  width: calc(100% - 80px);
}