Missed CSS in reply to buttons

## Bug Report

**Current Behavior**

https://discuss.flarum.org/d/27511-flarum-10-design-login-to-reply-issue

In the case the reply to button on a discussion is too long, for example for translated text, you should apply the following CSS:

```
overflow: hidden;
text-overflow: ellipsis;
```

This is used for left button "start topic" for example when user cannot start a topic but is not set for reply buttons so in my Italian community version Stable 1.0 the buttons for reply are showed badly.


**Steps to Reproduce**
You need use the nerata italian language and Flarum 1.0 than open as guest (not logged) a discussion and you will see the wrong reply button format.

**Expected Behavior**

Button should looks good not bad as the screenshot above.
The result should be:


**Environment**
- Flarum version: 1.0

```
Output of "php flarum info", run this in terminal in your Flarum directory.
```

**Possible Solution**

You need add

```
overflow: hidden;
text-overflow: ellipsis;
```

to

```
.DiscussionPage-nav .ButtonGroup, .DiscussionPage-nav .Button {
width: 100%;
}
```