The words ‘Elegance’ and ‘Simplicity’ characterise classic gardens.
There is always symmetry with formal lines and the inclusion of strong but limited elements.
Hard elements of pathways and edges are a feature of classic gardens as are formal elements at focal points like urns or fountains.
The use of colour is restricted and often relies on dark greens of foliage with white flowers. Topiarised plants are a feature.
Classic garden style is usually selected to harmonise with formal architecture. Think classic columns with arbours and climbers draping down, Camellias with soft pink flowers and a riot of blue Agapanthus under. Plant choices may be fluid dependant of climatic zones but the defining elements remain; symmetry, simplicity, restraint with an element of visual appeal at a focal point.