Toyser: Browser sandbox implementation

Following https://limpet.net/mbrubeck/2014/08/13/toy-layout-engine-3-css.html

Noted improvements in the tutorial

CSS

• multiple css selector declarations / matches.
• cascading stylesheets (source): stylesheets have hierarchy, so some should merge-or-override subsequent stylesheets' styles. To implement this, suggested:
  • Track the origin of each style
  • sort declarations by origin and importance
• computed CSS values: Many CSS values in browsers are not statically within stylesheets, but are calculated by the browser. A simple example is width: calc(50% - 10%)
• inheritance: An element should inherit its parents styles when it does not have the same key for itself.
• the style html attribute: any html element can have a style attribute to add styles to it. The specified_values style function could check for this and append values to whatever other values it finds.