Because innerHTML is potentially a security risk remove it from the code.

Here is simplest way to handle focus style that i can think of:

JS:

document.addEventListener('mousedown', () => { body.dataset.focus = '' })
document.addEventListener('keydown', e => { if (e.key === 'Tab') delete body.dataset.focus })

CSS:

body[data-focus] :focus {
  outline: 0;
}

body:not([data-focus]) :focus {
  outline: rgba(0, 125, 250, .6) solid 2px;
}

Benefits:

• doesn't create <style> element
• no css in js
• less code