1. Introduction

2. Three star-forming BCGs at \(z\sim0.4\)
2.1. The selection of the BCGs in KiDS
2.2. Stellar and star formation properties

3. IRAM 30m observations and data reduction

4. The comparison samples
4.1. Distant cluster galaxies observed in CO
4.2. Distant BCGs observed in CO
4.3. Galaxies with \(CO(1{\rightarrow}0)\) and \(CO(3{\rightarrow}2)\) observations

5. Results
5.1. Molecular gas properties
5.2. Gas fraction, star formation, and depletion time
5.3. Excitation ratios
5.4. Color-magnitude plots
5.5. Double-horn modeling for KiDS 1220. Structural parameters

6. Summary and conclusions