Based on your code I did more simplifications:
/* auto fades note header controlls */
.view-header:not(:hover) .view-actions {
opacity: 0.1;
transition: opacity .25s ease-in-out;
}
/* auto fades status bar items */
.status-bar:not(:hover) .status-bar-item {
opacity: 0.25;
transition: opacity .25s ease-in-out;
}
/* smaller scrollbar */
.CodeMirror-vscrollbar, .CodeMirror-hscrollbar, ::-webkit-scrollbar {
width: 3px;
height: 3px;
}
Edit1: Updated smaller scrollbar code to fix all scrollbars