Theme customization

Below you can see a demo of an editor with the dark theme as a result of customizations described later in this guide:

# Customization with CSS variables

Assuming you finished our quick start guide, and you have a running CKEditor 5 instance, let’s use the full potential of CSS variables (custom properties). The customization explained in this guide will make the theme dark, with slightly bigger text and more rounded corners.

The file containing custom variables can be named custom.css and it will look as below:

: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-dialog class colors. ----------------------------------- */

    --ck-color-dialog-background: var(--ck-custom-background);
    --ck-color-dialog-form-header-border: var(--ck-custom-border);

    /* -- 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-color-base-foreground);
    --ck-color-list-button-on-background: var(--ck-color-base-active);
    --ck-color-list-button-on-background-focus: var(--ck-color-base-active-focus);
    --ck-color-list-button-on-text: var(--ck-color-base-background);

    /* -- 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%);
}

Depending on your setup method, you can either import a style sheet into your js file:

import { ClassicEditor } from 'ckeditor5';

import 'ckeditor5/ckeditor5.css';

// Override the default styles.
import 'custom.css';

ClassicEditor
    .create( /* ... */ )
    .then( editor => {
        console.log( editor );
    } )
    .catch( err => {
        console.error( err.stack );
    } );

Or import it via the link in html in the CDN setup:

<link rel="stylesheet" href="path/to/custom.css" type="text/css">