- Changing styles for navigation bar

You can view the Pull Request on github:
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Opened By: SerhiiCho
Pull Request Description:
### Intro
Navigation bar is a little bit outdated for 2019, especially the mobile version. I think it's a good idea to make it look more **modern** for new people coming into the language. But at the same time don't make anything fancy and try to stick with the base structure. **Navigation bar** is a good place to start, but in future I'd like to continue with other parts as well. Just want to know your guys opinion about restyling [](<a href="" title=""></a>)

### Search bar on mobile view
The biggest change is that search bar is no longer visible on mobile view, instead there is a button with search icon on the left of the **navbar**. After first click it will show the search and **auto focus** on search input, but after second click it will try to **submit** the search form.

### Quick preview
![web-php](<a href="" title=""></a>)

_**Feel free to edit if you are a maintainer.**_