I work entirely on a small laptop, so always drag the sidebar to be as narrow as possible while still able to read most of the filename.
But with any reload of the page, Glitch sets it back to its original location.
I feel like when you pick up the toy a baby dropped and the baby just throws it right back down on the ground again… looks at you… and starts laughing at you.
Well, then you can write UserScript, that will set the drawer’s width to be equal some value, stored in localStorage and use any framework, that provides you executing scripts on external page (e.g. Tampermonkey):