In a nutshell, making a responsive website just requires the use of Media Queries. With additional CSS to overwrite default styles, you can create fully mobile friendly websites.

Using Flexbox, you can quickly and easily create vertically aligned text in a container.

Here’s an updated version of my Flexbox Responsive Menu with sub menus that open to the right. See the Pen Flexbox Menu Sub Menu by Richard (@barkins) on CodePen.

A quick reference guide for the CSS3 transition property.

With Flexbox, it’s relatively simple to quickly create a fully responsive menu without JavaScript. This example includes a one level drop down menu as well.