Posterior distribution of Horndeski parameters in the stable basis parametrised by ${\widehat{D}}_{\mathrm{kin}}$ and ${\widehat{c}}_{\mathrm{s}}^2$ for KiDS-Legacy (blue), Planck 2018 TTTEEE, low-ℓ TT, and low-ℓ EE (green), DESI DR2 BAO + eBOSS DR16 RSD (orange), and their combination (purple). Additionally, we show the posterior distribution of the braiding term at z = 0, α_B, 0, and the combination ${\widehat{c}}_{\mathrm{sN}}^2={\widehat{D}}_{\mathrm{kin}}{\widehat{c}}_{\mathrm{s}}^2$, which is derived from the sampling parameters. The black contour illustrates the prior volume. The inner and outer contours of the marginalised posteriors correspond to the 68% and 95% credible intervals, respectively. In the GR limit, these quantities converge to zero, as the Horndeski scalar field does not exist within GR.