Natyashastra
द्वारं तैनैव कोणेन कर्तव्यं तस्य वेश्मनः । द्वितीयं चैव कर्तव्यं रङ्गपीठस्य पृष्ठतः ॥ १०३॥
The door should be created using the same angles as the structure. A second door should also be constructed behind the stage (ranga-pitha).
english translation
dvAraM tainaiva koNena kartavyaM tasya vezmanaH । dvitIyaM caiva kartavyaM raGgapIThasya pRSThataH ॥ 103॥
hk transliteration by Sanscript