slots.html

<template>
    <article class="slds-card"><div class="slds-card__header slds-grid">
        <slot name="title">TITLE</slot>
    </div>
    <div class="slds-card__body slds-card__body_inner">
        <slot name="body">BODY</slot>
        <slot></slot>
    </div>
    </article>
</template>

slots.js

import { LightningElement } from 'lwc';

export default class Slots extends LightningElement {}

slots.js-meta.xml

<?xml version="1.0" encoding="UTF-8"?>
<LightningComponentBundle xmlns="http://soap.sforce.com/2006/04/metadata" fqn="slots">
    <apiVersion>45.0</apiVersion>
    <isExposed>false</isExposed>
</LightningComponentBundle>