bootstrap/reboot-shim.scss

// reboot-shim.scss
// This file provides just the selectors needed by _type.scss
// without including all of reboot.

h1, h2, h3, h4, h5, h6 { display: block; }
small { display: inline; }
mark { display: inline; }

a:not(.btn):not(.btn-link):link {
  color: var(--bs-link-color, #{$link-color});
}