Range inspectors have unreadable prefixes in light theme

### Tested versions

- Reproducible in: v4.5.beta7.official [4ebf67c12]
- Reproducible in: v4.4.1.stable.official [49a5bc7b6]

### System information

Godot v4.5.beta7 - Manjaro Linux `#1` SMP PREEMPT_DYNAMIC Mon, 01 Sep 2025 23:07:10 +0000 on Wayland - X11 display driver, Multi-window, 2 monitors - Vulkan (Forward+) - dedicated AMD Radeon RX 7600 (RADV NAVI33) - AMD Ryzen 5 5600 6-Core Processor (12 threads) - 15.54 GiB memory

### Issue description

On `Range` inspectors that have a prefix like Vector3 and particle ranges, the prefix is unreadable in light theme:

### Steps to reproduce

Use light theme

### Minimal reproduction project (MRP)

N/A

Start by reproducing the issue in Godot's light theme using Range inspectors with prefixes, such as Vector3 and particle ranges. Trace the editor UI code responsible for rendering these prefixes and compare the light-theme appearance with the dark theme. Done means the prefixes are readable in the light theme without regressing the affected inspectors.

Written by the indexing model from the issue text.