The correct way would be to extend \Illuminate\Support\Debug\HtmlDumper and add your custom styles there:
protected $styles = array(
'default' => 'background-color:#fff; color:#222; line-height:1.2em; font-weight:normal; font:12px Monaco, Consolas, monospace; word-wrap: break-word; white-space: pre-wrap; position:relative; z-index:100000',
'num' => 'color:#a71d5d',
'const' => 'color:#795da3',
'str' => 'color:#df5000',
'cchr' => 'color:#222',
'note' => 'color:#a71d5d',
'ref' => 'color:#a0a0a0',
'public' => 'color:#795da3',
'protected' => 'color:#795da3',
'private' => 'color:#795da3',
'meta' => 'color:#b729d9',
'key' => 'color:#df5000',
'index' => 'color:#a71d5d',
);
In order to add in the CSS I suggested, you would add this to the bottom of that array:
'compact' => 'display: block !important'
However, then you would also need to extend \Illuminate\Support\Debug\Dumper and make it use your custom HtmlDumper. You would also need to override the dd function to make it use your custom \Illuminate\Support\Debug\Dumper. It seems it may take a little more than should be necessary to accomplish the custom CSS.
The quick/dirty/easy way would be to just override your dd function and throw it in there, remember that you would need to place this somewhere where it gets loaded before Laravel does.
function dd()
{
if (PHP_SAPI !== 'cli')
{
echo "<style>pre.sf-dump .sf-dump-compact { display: block !important; }</style>";
}
array_map(function($x) { (new Dumper)->dump($x); }, func_get_args());
die;
}