Implement Breakpoints

[code-warrior]

Give the user the option to change the following breakpoints, whose values are inspired by the BBC’s GEL (Global Experience Language) for Grids:

• breakpoint--x-small: 400px;
• breakpoint--small: 600px;
• breakpoint--medium: 900px;
• breakpoint--large: 1008px;
• breakpoint--x-large: 1280px;

Also, give the user the option to toggle each or all of the breakpoints.