How to write a configurable component class that controls an element's aspect-ratio by specifying some custom variables.
Topic: CSS – Page 11
A clever CSS rule combining
:placeholder-shownto show validation state of non-empty input elements.
Elements with overflow: hidden are scroll containers and can be scrolled programmatically.
The ex unit stands for x-height and refers to height of the lowercase "x" character of a font.
The defined pseudo class can be used to style not defined custom elements.