I prefer a dark theme for my Manjaro linux, but that theme is bad for lazarus :-(
No, dark theme is not bad for Lazarus. But default colors look bad in message window when theme is dark. I solve it simply by applying dark pastel colors.
Long time ago I have added alternative harmonic light pastel colors to Lazarus message window since I have found original colors too distracting. These look very good on light OS theme with black font. Later I used dark OS theme and for white font different colors were needed so I have also created dark pastel colors. Unfortunately I didn't contribute them to Lazarus yet. That is not a problem since you can do it yourself. Replace default (R, G, B) Header Colors for Background with (35, 39, 41), for Running with (129, 100, 0), for Success with (9, 88, 0), for Failed with (128, 0, 3), and Scrolled Up with (0, 10, 85) and you will have Message window Header Colors as shown in the screenshot. You can also adapt Message Colors to your liking if you wish.
Light pastel colors history:
https://forum.lazarus.freepascal.org/index.php/topic,27412.msg170391.html#msg170391Attached screenshots are from Manjaro XFCE having Adwait-dark style with message window showing dark pastel colors mentioned above.