Button focus not consistent in button groups

Second, third, etc buttons in button groups don't get the outer box shadow on focus. 

Can be fixed with 

``` scss
&:focus {
  box-shadow: 0 0 5px rgba(81,167,232,0.5), inset 1px 0 0 rgba(255,255,255,0.2);
}
```

before the 

``` scss
&:active,
&.selected {
  box-shadow: inset 0 3px 5px rgba(0, 0, 0, 0.15);
}
```

in the `_buttons.scss` file (line 315ish).
