一笔一画勾勒曾经一心一意回想过去
[yī bĭ yī huà gōu lè céng jīng yī xīn yī yì huí xiăng guò qù]
It could be interpreted as 'Sketching out past memories bit by bit with undivided attention'. It describes recalling memories from the past slowly and carefully as though drawing every single moment with deep reflection, showing dedication to remembering what once was important in detail and entirety.