Inconsistent focus styling for select and link elements in modern color scheme

[ocean90]

Related: #50504

I noticed some inconsistency in the focus styling with the modern color scheme. See the attached screenshots and the one from the block editor.

Would be nice to use the same styling for all elements.

[justinahinon]

I went through the various parts of th admin with the modern color scheme activated.

I summarize here the different colors and box shadow properties use for inputs, buttons, checkboxes, links: ​https://docs.google.com/document/d/131OsbY0L0RTOUTXYvVeQc9Z5okFsNYj7rTJL_692QnA/edit?usp=drivesdk

I'll send a first fix next week.