Fashion girls take note: sensible dressing is major right now. When Alexa took to Insta last week to celebrate her preppy mom look, we were hooked — and even though khaki bombers and frayed denim might be trending right now, nerdy dressing is also going to fly this summer. Need a runway reference? Take a look at Gucci Fall '15. A little bit grandma, a whole lotta '70s geek — the collection took mannish or flared pants, knitted tank tops and mega-long A-line skirts and made them all totally relevant again. Here are the eight pieces you'll need to get involved…