Not a dumb question.. glad you asked. It is not a simple change, but doable.
You have to adjust the sizing in two places:
1) in the weather-screen-{color}-{width}.css (i.e. your 2023-6-weather-screen-taupe-narrow.css)
.leftSideBar {
width:9.5em;
2) in flyout-menu.php in the genCSSFlyout() function, there are a couple of width: statements which will have to be tweaked
Be aware that the sidebar menu was heavily tweaked to have the flyout menu work with CSS alone (no JavaScript needed), so do your changes proportionally to the values there to keep the aspect/operation of the menu working correctly.