Is right, Joanna, but I think is exactly Anagallis arvensis. I exclude the other species of the genus, presents in Sardinia off course, on the base of the size of the flowers. A. monelli has greater flowers than A. arvensis; A. parviflora has everyday blue and small flowers, with sepals longer than petals; A. minima has tiny flowers; A. crassifolia has different shape of leafs and creamy-pink flowers; A. tenella has pink purple-stiped petals.
A. foemina is not present in Sardinia according to a recent study.
After that, we need certainly another better photo of the flower, so as we can exclude the last species.
"Fermati ogni tanto. Fermati e lasciati prendere dal sentimento di meraviglia davanti al mondo". Tiziano Terzani