n-st created a pull request in webrender/trello-collapse-lists

Only show toggle icon when hovering over list header

*Part of a set of PRs: subtle icons #3, autohiding #4, or both #5.* I found it a bit too intrusive to have an icons to the left of each list title all the time (my intent behind collapsing lists is having less clutter, after all), so here's a patch to hide the icons by default and only show them when the mouse is hovered over a list header.
02 27, 2019