Intro sectio having a dropdown navigation

Interesting challenge. I botched the JS as i should have applied more DRY to my code, I decided in the end to leave it as is. If it works it works. Could probably pay more attention to media queries in the future as there`s a slight misarrangement when going desktop to tablet. Also I still cant figure a proper and elegant way to apply opacity so that the document darkens when the mobile side menu opens. Any feedback is always appreciated. Thanks.