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guideTheme customization

The default theme of CKEditor 5 can be customized to match most visual integration requirements.

Below, you can see an editor with the dark theme as a result of customizations described in a dedicated guide.

This is CKEditor 5.

It uses the default Lark theme with various customizations.

# Editor example configuration

View editor configuration script
import ClassicEditor from '@ckeditor/ckeditor5-editor-classic/src/classiceditor';
import Essentials from '@ckeditor/ckeditor5-essentials/src/essentials';
import Autoformat from '@ckeditor/ckeditor5-autoformat/src/autoformat';
import BlockQuote from '@ckeditor/ckeditor5-block-quote/src/blockquote';
import Bold from '@ckeditor/ckeditor5-basic-styles/src/bold';
import Heading from '@ckeditor/ckeditor5-heading/src/heading';
import Image from '@ckeditor/ckeditor5-image/src/image';
import ImageCaption from '@ckeditor/ckeditor5-image/src/imagecaption';
import ImageStyle from '@ckeditor/ckeditor5-image/src/imagestyle';
import ImageToolbar from '@ckeditor/ckeditor5-image/src/imagetoolbar';
import Indent from '@ckeditor/ckeditor5-indent/src/indent';
import Italic from '@ckeditor/ckeditor5-basic-styles/src/italic';
import Link from '@ckeditor/ckeditor5-link/src/link';
import List from '@ckeditor/ckeditor5-list/src/list';
import MediaEmbed from '@ckeditor/ckeditor5-media-embed/src/mediaembed';
import Paragraph from '@ckeditor/ckeditor5-paragraph/src/paragraph';
import EasyImage from '@ckeditor/ckeditor5-easy-image/src/easyimage';
import ImageUpload from '@ckeditor/ckeditor5-image/src/imageupload';
import CloudServices from '@ckeditor/ckeditor5-cloud-services/src/cloudservices';

ClassicEditor
    .create( document.querySelector( '#snippet-classic-editor' ), {
        plugins: [ Essentials,
            Autoformat,
            BlockQuote,
            Bold,
            Heading,
            Image,
            ImageCaption,
            ImageStyle,
            ImageToolbar,
            Indent,
            Italic,
            Link,
            List,
            MediaEmbed,
            Paragraph,
            EasyImage,
            ImageUpload,
            CloudServices ],
        toolbar: {
            items: [
                'heading',
                '|',
                'bold',
                'italic',
                'link',
                'bulletedList',
                'numberedList',
                '|',
                'outdent',
                'indent',
                '|',
                'blockQuote',
                'undo',
                'redo'
            ]
        },
        image: {
            toolbar: [ 'imageStyle:inline', 'imageStyle:block', 'imageStyle:side', '|', 'toggleImageCaption', 'imageTextAlternative' ]
        },
        cloudServices: {
            // This editor configuration includes the Easy Image feature.
            // Provide correct configuration values to use it.
            tokenUrl: 'https://example.com/cs-token-endpoint',
            uploadUrl: 'https://your-organization-id.cke-cs.com/easyimage/upload/'
            // Read more about Easy Image - https://ckeditor.com/docs/ckeditor5/latest/features/images/image-upload/easy-image.html.
            // For other image upload methods see the guide - https://ckeditor.com/docs/ckeditor5/latest/features/images/image-upload/image-upload.html.
        }
    } )
    .then( editor => {
        window.editor = editor;
    } )
    .catch( err => {
        console.error( err.stack );
    } );
View editor css style listing
:root {
    /* Overrides the border radius setting in the theme. */
    --ck-border-radius: 4px;

    /* Overrides the default font size in the theme. */
    --ck-font-size-base: 14px;

    /* Helper variables to avoid duplication in the colors. */
    --ck-custom-background: hsl(270, 1%, 29%);
    --ck-custom-foreground: hsl(255, 3%, 18%);
    --ck-custom-border: hsl(300, 1%, 22%);
    --ck-custom-white: hsl(0, 0%, 100%);

    /* -- Overrides generic colors. ------------------------------------------------------------- */

    --ck-color-base-foreground: var(--ck-custom-background);
    --ck-color-focus-border: hsl(208, 90%, 62%);
    --ck-color-text: hsl(0, 0%, 98%);
    --ck-color-shadow-drop: hsla(0, 0%, 0%, 0.2);
    --ck-color-shadow-inner: hsla(0, 0%, 0%, 0.1);

    /* -- Overrides the default .ck-button class colors. ---------------------------------------- */

    --ck-color-button-default-background: var(--ck-custom-background);
    --ck-color-button-default-hover-background: hsl(270, 1%, 22%);
    --ck-color-button-default-active-background: hsl(270, 2%, 20%);
    --ck-color-button-default-active-shadow: hsl(270, 2%, 23%);
    --ck-color-button-default-disabled-background: var(--ck-custom-background);

    --ck-color-button-on-background: var(--ck-custom-foreground);
    --ck-color-button-on-hover-background: hsl(255, 4%, 16%);
    --ck-color-button-on-active-background: hsl(255, 4%, 14%);
    --ck-color-button-on-active-shadow: hsl(240, 3%, 19%);
    --ck-color-button-on-disabled-background: var(--ck-custom-foreground);

    --ck-color-button-action-background: hsl(168, 76%, 42%);
    --ck-color-button-action-hover-background: hsl(168, 76%, 38%);
    --ck-color-button-action-active-background: hsl(168, 76%, 36%);
    --ck-color-button-action-active-shadow: hsl(168, 75%, 34%);
    --ck-color-button-action-disabled-background: hsl(168, 76%, 42%);
    --ck-color-button-action-text: var(--ck-custom-white);

    --ck-color-button-save: hsl(120, 100%, 46%);
    --ck-color-button-cancel: hsl(15, 100%, 56%);

    /* -- Overrides the default .ck-dropdown class colors. -------------------------------------- */

    --ck-color-dropdown-panel-background: var(--ck-custom-background);
    --ck-color-dropdown-panel-border: var(--ck-custom-foreground);

    /* -- Overrides the default .ck-splitbutton class colors. ----------------------------------- */

    --ck-color-split-button-hover-background: var(--ck-color-button-default-hover-background);
    --ck-color-split-button-hover-border: var(--ck-custom-foreground);

    /* -- Overrides the default .ck-input class colors. ----------------------------------------- */

    --ck-color-input-background: var(--ck-custom-background);
    --ck-color-input-border: hsl(257, 3%, 43%);
    --ck-color-input-text: hsl(0, 0%, 98%);
    --ck-color-input-disabled-background: hsl(255, 4%, 21%);
    --ck-color-input-disabled-border: hsl(250, 3%, 38%);
    --ck-color-input-disabled-text: hsl(0, 0%, 78%);

    /* -- Overrides the default .ck-labeled-field-view class colors. ---------------------------- */

    --ck-color-labeled-field-label-background: var(--ck-custom-background);

    /* -- Overrides the default .ck-list class colors. ------------------------------------------ */

    --ck-color-list-background: var(--ck-custom-background);
    --ck-color-list-button-hover-background: var(--ck-custom-foreground);
    --ck-color-list-button-on-background: hsl(208, 88%, 52%);
    --ck-color-list-button-on-text: var(--ck-custom-white);

    /* -- Overrides the default .ck-balloon-panel class colors. --------------------------------- */

    --ck-color-panel-background: var(--ck-custom-background);
    --ck-color-panel-border: var(--ck-custom-border);

    /* -- Overrides the default .ck-toolbar class colors. --------------------------------------- */

    --ck-color-toolbar-background: var(--ck-custom-background);
    --ck-color-toolbar-border: var(--ck-custom-border);

    /* -- Overrides the default .ck-tooltip class colors. --------------------------------------- */

    --ck-color-tooltip-background: hsl(252, 7%, 14%);
    --ck-color-tooltip-text: hsl(0, 0%, 93%);

    /* -- Overrides the default colors used by the ckeditor5-image package. --------------------- */

    --ck-color-image-caption-background: hsl(0, 0%, 97%);
    --ck-color-image-caption-text: hsl(0, 0%, 20%);

    /* -- Overrides the default colors used by the ckeditor5-widget package. -------------------- */

    --ck-color-widget-blurred-border: hsl(0, 0%, 87%);
    --ck-color-widget-hover-border: hsl(43, 100%, 68%);
    --ck-color-widget-editable-focus-background: var(--ck-custom-white);

    /* -- Overrides the default colors used by the ckeditor5-link package. ---------------------- */

    --ck-color-link-default: hsl(190, 100%, 75%);
}
View editor content listing
<div id="snippet-classic-editor">
    Editor content is inserted here.
</div>