For an inside mount, these UFURMATE Inside Mount Brackets would work well ... you can either buy an existing blackout roller shade like this Mainstays Blackout Tear-to-Fit Shade from Walmart ...

SwitchBot's Roller Shade offers smooth operation and is effective at blocking sunlight. Installation may be cumbersome if ...

DURABLE METAL CONSTRUCTION: Made from high-quality metal, these brackets are designed to ... and install the screws to securely mount your roller shades. Bracket size is 1.2 x 1.2 inches.