helloWorld.html

<template>
    <lightning-card title="HelloWorld" icon-name="custom:custom14">
        <div class="slds-m-around_medium">
            <p>Hello, {upperCaseName}!</p>
            <lightning-input name="last_name" label="Last Name" onchange={changeHandler}></lightning-input>
            <template if:false={showLastNameOnly}>
                <div>
                        <lightning-input name="first_name" label="First Name" onchange={changeHandler}></lightning-input>
                </div>
            </template>
            <lightning-input type="checkbox" label="Show Last Name only" onchange={handleCheckBox}></lightning-input>
        </div>
    </lightning-card>
</template>