@ckeditor/ckeditor5-list/theme/todolist.css

/*
 * Copyright (c) 2003-2022, CKSource Holding sp. z o.o. All rights reserved.
 * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
 */

:root {
	--ck-todo-list-checkmark-size: 16px;
}

.ck-content .todo-list {
	list-style: none;

	& li {
		margin-bottom: 5px;

		& .todo-list {
			margin-top: 5px;
		}
	}

	& .todo-list__label {
		& > input {
			-webkit-appearance: none;
			display: inline-block;
			position: relative;
			width: var(--ck-todo-list-checkmark-size);
			height: var(--ck-todo-list-checkmark-size);
			vertical-align: middle;

			/* Needed on iOS */
			border: 0;

			/* LTR styles */
			left: -25px;
			margin-right: -15px;
			right: 0;
			margin-left: 0;

			&::before {
				display: block;
				position: absolute;
				box-sizing: border-box;
				content: '';
				width: 100%;
				height: 100%;
				border: 1px solid hsl(0, 0%, 20%);
				border-radius: 2px;
				transition: 250ms ease-in-out box-shadow, 250ms ease-in-out background, 250ms ease-in-out border;
			}

			&::after {
				display: block;
				position: absolute;
				box-sizing: content-box;
				pointer-events: none;
				content: '';

				/* Calculate tick position, size and border-width proportional to the checkmark size. */
				left: calc( var(--ck-todo-list-checkmark-size) / 3 );
				top: calc( var(--ck-todo-list-checkmark-size) / 5.3 );
				width: calc( var(--ck-todo-list-checkmark-size) / 5.3 );
				height: calc( var(--ck-todo-list-checkmark-size) / 2.6 );
				border-style: solid;
				border-color: transparent;
				border-width: 0 calc( var(--ck-todo-list-checkmark-size) / 8 ) calc( var(--ck-todo-list-checkmark-size) / 8 ) 0;
				transform: rotate(45deg);
			}

			&[checked] {
				&::before {
					background: hsl(126, 64%, 41%);
					border-color: hsl(126, 64%, 41%);
				}

				&::after {
					border-color: hsl(0, 0%, 100%);
				}
			}
		}

		& .todo-list__label__description {
			vertical-align: middle;
		}
	}
}

/* RTL styles */
[dir="rtl"] .todo-list .todo-list__label > input {
	left: 0;
	margin-right: 0;
	right: -25px;
	margin-left: -15px;
}

/*
 * To-do list should be interactive only during the editing
 * (https://github.com/ckeditor/ckeditor5/issues/2090).
 */
.ck-editor__editable .todo-list .todo-list__label > input {
	cursor: pointer;

	&:hover::before {
		box-shadow: 0 0 0 5px hsla(0, 0%, 0%, 0.1);
	}
}