Chord sequence
D♯m7 D7 C♯maj7
In every key
Four-note rootless voicings in their two forms, with the 3rd or the 7th on the bottom, played over the root.
Heard in C# major
All the chords
The ii-V-I with a tritone substitute: bII7 in place of V7, so the bass falls by half steps from ii to I.
Over D#m7 · ii7
Mode 2 of Major
Over D7 · subV7
Mode 4 of Melodic Minor
Over C#maj7 · Imaj7
The major scale and its modes are the most commonly used scales in western music.