Get started building custom themes

In this example, you will create a basic theme extension where you’ll modify the font size and the primary colors.

Custom themes contain the following elements:

  • A definition (QEXT) file
  • A main JSON file
  • Optional assets

Creating the container

Create a folder that will contain your assets and name it my-custom-theme.

Creating the definition file

The definition file defines how custom themes are loaded in Qlik Sense.

The QEXT file extension must be in lower case letters, as in my-custom-theme.qext.

Tip: Make sure your QEXT file is a valid JSON file.

JSON validator:

The following properties are mandatory for a valid custom theme definition file:

Definition file properties

nameThe name of the custom theme.
typeExetension type. Should always be theme for custom themes.

Tip: Add additional properties to the QEXT file as it can provide helpful information about the custom component.


Create a QEXT file in the folder you just created and name it my-custom-theme.qext.

It should contain the following information:

    "name": "Custom theme",
    "description": "My first custom theme",
    "type": "theme",
    "version": "1.0.0",
    "author": "Qlik"

Creating the main JSON file

In the JSON file, you define the style for the individual visualization types. Create a main JSON file and place it in the same folder as the QEXT file. Name it theme.json, paste the following code into the JSON file, and then save it.

  "_inherit": true,
  "_variables" : {
    "@greenColor" : "#61a729",
    "@text": "#4c4c4c"
  "color": "@text",
  "fontSize": "12px",
  "object" : {
    "title": {
      "main": {
        "fontSize" : "16px"
  "dataColors": {
    "primaryColor": "@greenColor"

See Custom theme JSON properties for more details on creating the JSON file and its properties.

Prefixing custom themes

It is good practice to prefix your custom themes to prevent conflicts with custom themes created by other developers.

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