For changing text such as labels and other things that are part of WordPress or a theme, you need to do translation. This theme is translation ready, as-is WordPress, but you have to translate it using the included language file celestial.pot in the theme’s language file. I would recommend searching WordPress for translating. There are also plugins you can use for translating such as http://wpml.org/ (although I think this one is a paid one).
For the search widget…seems fine when I view your site but I will check it out again. I may need to recode it so that it has better responsive form fields…I did this for the Celestial Reloaded theme a couple weeks ago.
For widget style 4, you need to add a colour to it. So the class would be for example, red:
You have the colours: red, amber, purple, mycustom (custom colour set in the theme options). However, it sounds like what you want is just a border only. So you need to do some custom css instead of using a widget class method as outlined above. You would need to do something like this and to target that specific widget: