Poor contrast of current line highlight in "Dark" theme

[per1234]

Describe the problem

The current line in the Arduino IDE editor is indicated by a difference in the background color (AKA "highlight") of that line.

When using the "Dark" theme, the contrast between the color of the highlight and the background color of the rest of the editor is very low.

🐛 Users may have difficulty distinguishing the background, or not be able to see it at all (especially users with visual impairments).

To reproduce

1. Select File > Preferences... (or Arduino IDE > Settings... for macOS users) from the Arduino IDE menus.
   The "Preferences" dialog will open.
2. Select "Dark" from the "Theme" menu in the "Preferences" dialog.
3. Click the "OK" button.

🐛 The highlight at the current line in the editor has poor contrast against the editor background:

(the highlight is on line 2 in the screenshot)

Expected behavior

The color of the current line highlight has sufficient contrast.

Arduino IDE version

5fd02b9

Operating system

Windows

Operating system version

11

Additional context

The demonstration above uses the highlight as an indication of editing position for the sake of simplicity. However, this is not a very compelling demonstration of the fault because the cursor also usually provides an indication of the current editing position, so the user may not be significantly impacted by the loss of an additional indicator of position.

A more impactful manifestation of the defect is when using the debugger. In this case, the current line highlight indicates the execution position when stepping. In this case, the cursor will not serve as an additional indicator so the highlight is the sole indicator of this crucial information. The user reports were in the context of using the debugger.

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The highlight has good contrast when using the other officially supported IDE themes.

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You must have the editor.renderLineHighlight advanced setting set to "line" (the default) or "all" in order to reproduce the demonstration.

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Originally reported by @KurtE at https://forum.arduino.cc/t/adding-debug-support-to-a-non-arm-eabi-board-type/1138076/9

Additional Reports

• https://forum.arduino.cc/t/mkr-zero-atmel-ice-win11-ide-2-1-1-fault/1158711/3
• https://forum.arduino.cc/t/debugging-is-not-really-working/1168093
• https://forum.arduino.cc/t/any-plans-to-document-ide-debugger-ui-usage/1227970

Workaround

1. Select File > Preferences... (or Arduino IDE > Settings... for macOS users) from the Arduino IDE menus.
   The "Preferences" dialog will open.
2. Select anything other than "Dark" from the "Theme" menu in the "Preferences" dialog.
3. Click the OK button.

Issue checklist

• I searched for previous reports in the issue tracker
• I verified the problem still occurs when using the latest nightly build
• My report contains all necessary details