How to add Custom setting in Liferay Theme

init_custom.ftl

<#--
This file allows you to override and define new FreeMarker variables.
-->
<#assign
	
	show_header = getterUtil.getBoolean(themeDisplay.getThemeSetting("show-header"))
	
/>

liferay-look-and-feel.xml

<?xml version="1.0"?>
<!DOCTYPE look-and-feel PUBLIC "-//Liferay//DTD Look and Feel 7.3.0//EN" "http://www.liferay.com/dtd/liferay-look-and-feel_7_3_0.dtd">

<look-and-feel>
	<compatibility>
		<version>7.3.0+</version>
	</compatibility>
	<theme id="my-website" name="my-website">
		<template-extension>ftl</template-extension>
		<settings>
			<setting configurable="true" key="show-header" type="checkbox" value="true" />
		</settings>
		<portlet-decorator id="barebone" name="Barebone">
			<default-portlet-decorator>true</default-portlet-decorator>
			<portlet-decorator-css-class>portlet-barebone</portlet-decorator-css-class>
		</portlet-decorator>
		<portlet-decorator id="borderless" name="Borderless">
			<portlet-decorator-css-class>portlet-borderless</portlet-decorator-css-class>
		</portlet-decorator>
		<portlet-decorator id="decorate" name="Decorate">
			<portlet-decorator-css-class>portlet-decorate</portlet-decorator-css-class>
		</portlet-decorator>
	</theme>
</look-and-feel>

portal_normal.ftl

 <#if show_header && !is_signed_in>
  <header class="header fixed-header">
  <#else>
  <header class="header">
  </#if>