Question: Does it simply mean that I have a parameter in my 'model\_params' variable that is not in this line?

```
params.require(...).permit(...)

```

I can't find offending parameter. Is there a way to accept all parameters?

Answer: 
A space is a [descendant combinator](https://www.w3.org/TR/css3-selectors/#descendant-combinators). It targets descendants, but the div is not a descendant of the button, it is a sibling.

You need to use the [adjacent sibling combinator](https://www.w3.org/TR/css3-selectors/#adjacent-sibling-combinators) instead: a plus sign.

You also need to target the links (which are descendants of `.dropcontent` so you should use a descendant combinator there) since it is those which you have set `display: none` on and not the div.

```
.dropbutton:hover + .dropcontent a {

```
I'd move the `display: none;` to the `.dropcontent` itself - as it now pertains to its anchors, that is, links, and as such, neither current answer would work -, then use 

```
.dropbutton:hover + .dropcontent
{
    display: block;
}

```

But you must not add anything between dropbutton and dropcontent afterwards, or it will not work any more.