A better way to customize basic style

[Kikobeats]

Right now is a bit complicated setup custom style for card look and feel from the vanilla connector:

   <style>
    .microlink_hover,
    .microlink_card,
    .microlink_hover:hover,
    .microlink_card:hover {
      background: #1A1A1A !important;
      color: white;
    }

    .microlink_hover {
      border-color: #666 !important;
    }

    .microlink_hover:hover {
      border-color: #999 !important;
    }

   </style>

It's necessary to use !importannt because the styled is encapsulated into the react wrapper so you can't override it directly.

A better approach there could move basic CSS properties into CSS variables, easy overwriting the default value:

<style>
:root {
  --microlink-card-bg-color: black;
  --microlink-card-color: white;
  --microlink-card-border-color: #666;
  --microlink-card-border-hover-color: #999;
}
</style>

That should be also a simple way for supporting theming out of the box, resolving #81