Nodeless kagome superconductivity in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>LaRu</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:msub><mml:mi>Si</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math>

We report muon spin rotation (${\mu}$SR) experiments together with first-principles calculations on microscopic properties of superconductivity in the kagome superconductor LaRu$_3$Si$_2$ $T_{\rm c}$ ${\simeq}$ 7K. find that calculated normal state band structure features a flat and Dirac as well van Hove points formed by Ru-$dz^2$ orbitals near Fermi level. Below c}$, ${\mu}$SR reveals isotropic type-II superconductivity, which is robust against hydrostatic pressure up to 2 GPa. Intriguingly, ratio 2$\Delta/k_{\rm B}T_{\rm 4.3 (where ${\Delta}$ superconducting energy gap) strong coupling limit, c}$/$\lambda_{eff}^{-2}$ ${\lambda}$ penetration depth) comparable high-temperature unconventional superconductors. also electron-phonon alone can only reproduce small fraction from calculations, suggests other factors enhancing such correlation effect band, point lattice, high density states narrow bands. Our taken nature LaRu$_3$Si$_2$.