Basic event handling. Not going to bubble though there are event listeners wrapping the button. {bubbles: false, composed : false} [Default config]

app.html

<template>
    <c-child></c-child>
</template>

app.js

import { LightningElement, track } from 'lwc';

export default class App extends LightningElement {
    
}

child.html

<template>

    <section onteja={handleTeja}>
        <div onteja={handleTeja}>
            <span onteja={handleTeja}>
                <lightning-button label="Send" onclick={handleSend}>
                    </lightning-button>

            </span>
        </div>
    </section>
</template>

child.js

import { LightningElement, api } from 'lwc';

/**
 * Show an item
 */
export default class Child extends LightningElement {
    handleSend(){

        this.template.querySelector('span')
            .dispatchEvent(new CustomEvent('teja'))
    }

    handleTeja(){
        console.log('AM IN TEJA!!!!!');
    }
}