Flexing CSS flex creating time-responsive data charts

** General Comments **

• Feel free to suggest advise!
• loved the addition of a javascript element, lots of fun making charts

** Things to work on/ ask about **

• i used flex a lot on this project ( see html that says horizontally/vertically for different flex directions), i did use some CSS magic to get the brown popup by reversing the flex direction (see vertical-reverse), i was wondering if there was a better way to code this
• also wondering if my js code can be cleaned up in fewer lines.
• looking for a better way to name my html tags, can anyone suggest a good naming system?