Poor visibility of keyboard focus indicator on buttons in Mint-Y theme

Issue: Poor visibility of keyboard focus indicator on buttons in Mint-Y theme

Description:
In the Mint-Y theme (both light and dark variants), the visual indicator that shows which button has keyboard focus is difficult to see. The focus style uses a subtle border or low‑contrast color that does not meet WCAG AA contrast requirements for focus visibility.

Steps to reproduce:

1. Launch any GTK application that uses the Mint-Y theme (e.g., gnome-control-center with the theme set).
2. Navigate to a dialog containing multiple buttons using the Tab key.
3. Observe the focus outline on the currently focused button.

Expected behavior:
The focused button should display a clear, high‑contrast focus indicator (e.g., a 2 px solid outline in a color that contrasts with both the button background and the surrounding UI).

Actual behavior:
The focus indicator is a thin, low‑contrast line (often 1 px, color close to the button background) making it hard to discern which button is focused, especially for users with low vision or in bright lighting conditions.

Suggested fix:
Modify the button focus rule in the theme’s GTK CSS to increase the outline width and/or change its color to a higher contrast value.

Example change in gtk-3.0/gtk.css (and gtk-dark.css if separate):

.button:focus {
    outline: 2px solid @focus_color; /* or a specific rgba value */
    outline-offset: 2px;
}

Where @focus_color could be #0060df (a strong blue) for the light theme and #4a90e2 for the dark theme, or use the symbolic color @theme_focus_color defined elsewhere in the theme.

Additional notes:

• The same issue may affect other widget types (e.g., entries, tabs) that rely on the generic .button focus style.
• After applying the change, run gtk-update-icon-cache -f /usr/share/themes/Mint-Y and restart the affected applications to see the update.
• Testing with accessibility tools (e.g., xrandr --output ... --brightness or high‑contrast themes) is recommended.

Environment:

• Linux Mint 21.3 (or any distro using Mint-Y theme)
• GTK version 3.24.x (as shipped with Mint)
• Theme version: latest from https://github.com/linuxmint/mint-themes

Start with the button focus rule in gtk-3.0/gtk.css and, if separate, gtk-dark.css. Test the Mint-Y theme in a GTK application such as gnome-control-center by moving focus with Tab, then verify that the indicator is clearly visible against both the button and surrounding UI in light and dark variants.