Inside the `theme(…)` function, we can use the `/` character for
applying an opacity. For example `theme(colors.red.500 / 50%)` will
apply a 50% opacity to the `colors.red.500` value.
However, if you used a variable instead of the hardcoded `50%` value,
then this was not parsed correctly. E.g.: `theme(colors.red.500 /
var(--opacity))`
_If_ we have this exact syntax (with the spaces), then it parses, but
some information is lost:
```html
<div class="bg-[theme(colors.red.500_/_var(--opacity))]"></div>
```
Results in:
```css
.bg-\[theme\(colors\.red\.500_\/_var\(--opacity\)\)\] {
background-color: color-mix(in srgb, #ef4444 calc(var * 100%), transparent);
}
```
Notice that the `var(--opacity)` is just parsed as `var`, and the
`--opacity` is lost.
Additionally, if we drop the spaces, then it doesn't parse at all:
```html
<div class="bg-[theme(colors.red.500/var(--opacity))]"></div>
```
Results in:
```css
```
This means that we have to handle 2 issues to make this work:
1. We have to properly handle the `/` character as a proper separator.
2. If we have sub-functions, we have to make sure to print them in full
(instead of only the very first node (`var` in this case)).
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