Built-in dark mode settings versus custom CSS overrides for low-vision accessibility in Kibana

The goal is to determine whether Kibana's built-in dark mode and high-contrast themes, configurable through the Settings UI, adequately support low-vision users without compromising responsive layout behavior, or whether custom CSS overrides provide necessary flexibility at the risk of breaking accessibility and responsiveness.

Built-in themes are designed to maintain the application's grid and component responsiveness, but they offer limited customization for individual color-perception needs. Custom CSS allows targeted adjustments to contrast, spacing, and font rendering, yet it can override established responsive breakpoints and alter the reading order that screen readers depend on. Version-specific implementations across Kibana 7.x, 8.x, and 9.x may further affect how themes are applied and cascaded.

How do custom CSS modifications interact with Kibana's responsive grid system in high-contrast mode? Does the Settings UI dark mode provide adequate color contrast ratios for typical low-vision user profiles? What version-specific differences exist between Kibana 7.x, 8.x, and 9.x in theme application and CSS cascade behavior?