Hi can you reduce the color palette items?
I have a suggestion for 15 default color, here is the hex code to ease you implement:
Currently the rectangle is too long, I don't like to scroll up and down to pick color.

paints: [
    '#00B16A',
    '#008C3A',
    '#66CC00',
    '#FFC114',
    '#F6630D',
    '#FF0066',
    '#E71224',
    '#AB69D3',
    '#DA28B9',
    '#c821e7',
    '#1073BE',
    '#00A0D7',
    '#33CCFF',
    '#000000',
    '#FFFFFF',
  ],

in your style.css

.tool-thin {
	width: 25px;
	height: 25px;
	border-style: dashed;
	border-color:#fff;
	transition: all 0.25s ease;
}

.tool-thin:hover,
.tool-thin.selected {
	border-style: solid;
	border-color:#fff;
}

now is missing undo + redo + eraser
Use a link list record what did the user draw might work for undo and redo
For the eraser, invisible brush of background color might work

Color pallete should be put at most left because when split view, the option will disappear