CSS numbers without units where units are necessary should cause a warning

In this case `top` and `left` should have units after their values.

```
#greeting {
background: rgb(255, 255, 0);
border: 2px solid black;
font-family: "Comic Sans MS", fantasy;
padding: 5px;
width: 262px;
position: absolute;
top: 100;
left: 20;
z-index: 2;
}
```

Use the CSS example in the issue as the acceptance case, focusing on the unitless `top: 100` and `left: 20` declarations. Trace the warning or validation entry point and verify that these declarations produce warnings while valid unit-bearing values and `z-index: 2` remain appropriate.

Written by the indexing model from the issue text.