Window Borders

Mosaico draws a colored border overlay around every visible tiled window. The focused window is highlighted with the focused (or monocle) color; every other tiled window on the active workspace gets a muted unfocused border so tile boundaries stay readable – especially with small gaps. Unfocused borders can be disabled if you prefer a minimal look.

Configuration

Border settings are in config.toml:

[borders]
width = 4              # Border thickness in pixels (0-32)
corner_style = "small" # "square", "small", or "round"

[borders.colors]
focused = "#00b4d8"    # Color for focused window in tiled layouts
monocle = "#2d6a4f"    # Color for focused window in monocle mode
unfocused = "#6c7086"  # Color drawn around unfocused tiled windows

width – thickness of the border in pixels. Set to 0 to disable every border.
corner_style – controls both the border overlay shape and the DWM corner preference for tiled windows (Windows 11 only; ignored on Windows 10).

Value Border overlay DWM (Windows 11)

"square" Sharp corners (0 px) DONOTROUND

"small" Subtle rounding (8 px) ROUNDSMALL (~4 px)

"round" Standard rounding (16 px) ROUND (~8 px)
borders.colors.focused – the border color for the focused window during normal tiling. Accepts hex colors or named theme colors (see Theming).
borders.colors.monocle – the border color when monocle mode is active.
borders.colors.unfocused – the border color drawn around every unfocused tiled window. Set to "none" to disable unfocused borders entirely (only the focused window will have a border in that case). An empty string falls back to the active theme’s muted-gray default.

Value	Border overlay	DWM (Windows 11)
`"square"`	Sharp corners (0 px)	`DONOTROUND`
`"small"`	Subtle rounding (8 px)	`ROUNDSMALL` (~4 px)
`"round"`	Standard rounding (16 px)	`ROUND` (~8 px)

Behavior

Every tiled window on every monitor’s active workspace gets its own border overlay.
Changing focus recolors the previously focused border to the unfocused color and the new focused border to the focused color, in one update.
Switching workspaces hides the outgoing windows’ borders and shows the incoming windows’ borders.
In monocle mode only the focused window’s border renders; all other tiled borders on that monitor are hidden until monocle is toggled off.
When the focused window is maximized, its border is hidden so it does not overflow off-screen, and unfocused borders on the same monitor are also hidden because they are visually covered.
Borders are click-through (WS_EX_TRANSPARENT) and never interfere with mouse interaction.

Using Named Colors

With a theme active, you can use named colors:

[borders.colors]
focused = "blue"
monocle = "green"
unfocused = "mauve"

Empty values fall back to the theme’s defaults: blue for focused, green for monocle, and a muted gray (Catppuccin Overlay0) for unfocused.

Disabling Unfocused Borders Only

If you want the focus highlight without borders on every other window:

[borders.colors]
unfocused = "none"

This keeps focused and monocle rendering as before and skips unfocused borders entirely. Use width = 0 instead if you want every border off.

Hot-Reload

Border settings are hot-reloaded. Changes to width, corner_style, and any [borders.colors] entry take effect immediately, including flipping unfocused = "none" on or off.