HTML/CSS - stopwatch setInterval clearInterval Online Editor and JavaScript Compiler

html

<!-- Created by Андрей Шумаков -->
<!--
https://www.sololearn.com/discuss/3104462
button-error
https://html.spec.whatwg.org/multipage/timers-and-user-prompts.html#timers
-->
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <!-- <link rel="stylesheet" href="style.css"> -->
    <title>stopwatch</title>
</head>
<body>
    <div class="stopwatch">Секундомер
        <div class="time" id="time">00:00:00:00:00.00</div>
        <button class="btn" id="start">Start</button>
        <button class="btn" id="pause">Pause</button>
        <button class="btn" id="reset">Reset</button>
    </div>
    <!-- <script src="app.js"></script> -->
</body>
</html>

css

/* Created by Андрей Шумаков */
@import url('https://fonts.googleapis.com/css2?family=JetBrains+Mono&display=swap');
body{
    background-color:  #cfcbcb;
}
.stopwatch{
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    text-align: center;
    
}
.stopwatch{
    background:  rgb(62,58,180);
    background: linear-gradient(43deg,  rgba(62,58,180,1)
                                0%,  rgba(29,167,253,1) 
                                50%,  rgba(196,69,252,1) 
                                100%);
    padding:  20px 20px;
    border-radius:  10px;
    border: 2px solid  rgb(65, 51, 210);
    box-shadow: 12px 12px 2px 1px  rgba(0, 0, 255, .2);
    color:  #fff;
    font-size: 28px;

// Created by Андрей Шумаков 
const 
time = document.querySelector('#time'),
start = document.querySelector('#start'),
pause = document.querySelector('#pause'),
reset = document.querySelector('#reset')
let mlsec=0, sec=0, min=0, hrs=0, day=0, year=0
var t = null;
function increaseTime() {
    ++mlsec 
    if (mlsec >= 100) {
        mlsec = 0
        ++sec 
        if (sec >= 60) {
            sec = 0 
            ++min
            if (min >= 60) {
                min = 0
                ++hrs
                if (hrs >= 24) {
                    hrs = 0
                    ++day
                    if (day >= 365) {
                        day = 0 
                        ++year

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