JSFiddle - React, Tailwind, and code Playground

by IvanGrishov

HTML

<h1 class="heading">сюда вывести выбранную дату</h1>
  <hr/><div class="light"><div class="calendar">
        <div class="calendar-header">
            <span class="month-picker" id="month-picker">February</span>
            <div class="year-picker">
                <span class="year-change" id="prev-year">
                    <pre><</pre>
                </span>
                <span id="year">2021</span>
                <span class="year-change" id="next-year">
                    <pre>></pre>
                </span>
            </div>
        </div>
        <div class="calendar-body">
            <div class="calendar-week-day">
                <div>Sun</div>
                <div>Mon</div>
                <div>Tue</div>
                <div>Wed</div>
                <div>Thu</div>
                <div>Fri</div>
                <div>Sat</div>
            </div>
            <div class="calendar-days"></div>
        </div>
        
        <div class="month-list"></div>
    </div>
  </div>

CSS

:root {
    --dark-body: #4d4c5a;
    --dark-main: #141529;
    --dark-second: #79788c;
    --dark-hover: #323048;
    --dark-text: #f8fbff;

    --light-body: #f3f8fe;
    --light-main: #fdfdfd;
    --light-second: #c3c2c8;
    --light-hover: #edf0f5;
    --light-text: #151426;

    --blue: #0000ff;
    --white: #fff;

    --shadow: rgba(100, 100, 111, 0.2) 0px 7px 29px 0px;

    --font-family: cursive;
}

.dark {
    --bg-body: var(--dark-body);
    --bg-main: var(--dark-main);
    --bg-second: var(--dark-second);
    --color-hover: var(--dark-hover);
    --color-txt: var(--dark-text);
}

.light {
    --bg-body: var(--light-body);
    --bg-main: var(--light-main);
    --bg-second: var(--light-second);
    --color-hover: var(--light-hover);
    --color-txt: var(--light-text);
}

* {
    padding: 0;
    margin: 0;
    box-sizing: border-box;
}

html,
body {
    height: 100vh;
    display: grid;
    place-items: center;
    font-family: var(--font-family);
    background-color: var(--bg-body);
}

.calendar {
    height: max-content;
    width: max-content;
    background-color: var(--bg-main);
    border-radius: 30px;
    padding: 20px;
    position: relative;
    overflow: hidden;
    /* transform: scale(1.25); */
}

.light .calendar {
    box-shadow: var(--shadow);
}

.calendar-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    font-size: 25px;
    font-weight: 600;
    color: var(--color-txt);
    padding: 10px;
}

.calendar-body {
    padding: 10px;
}

.calendar-week-day {
    height: 50px;
    display: grid;
    grid-template-columns: repeat(7, 1fr);
    font-weight: 600;
}

.calendar-week-day div {
    display: grid;
    place-items: center;
    color: var(--bg-second);
}

.calendar-days {
    display: grid;
    grid-template-columns: repeat(7, 1fr);
    gap: 2px;
    color: var(--color-txt);
}

.calendar-days div {
    width: 50px;
    height: 50px;
    display: flex;
    align-items: center;
    justify-content:...

JavaScript

let calendar = document.querySelector('.calendar')

const month_names = ['January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October', 'November', 'December']

isLeapYear = (year) => {
    return (year % 4 === 0 && year % 100 !== 0 && year % 400 !== 0) || (year % 100 === 0 && year % 400 ===0)
}

getFebDays = (year) => {
    return isLeapYear(year) ? 29 : 28
}

generateCalendar = (month, year) => {

    let calendar_days = calendar.querySelector('.calendar-days')
    let calendar_header_year = calendar.querySelector('#year')

    let days_of_month = [31, getFebDays(year), 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]

    calendar_days.innerHTML = ''

    let currDate = new Date()
    if (!month) month = currDate.getMonth()
    if (!year) year = currDate.getFullYear()

    let curr_month = `${month_names[month]}`
    month_picker.innerHTML = curr_month
    calendar_header_year.innerHTML = year

    // get first day of month
    
    let first_day = new Date(year, month, 1)

    for (let i = 0; i <= days_of_month[month] + first_day.getDay() - 1; i++) {
        let day = document.createElement('div')
        if (i >= first_day.getDay()) {
            day.classList.add('calendar-day-hover')
            day.innerHTML = i - first_day.getDay() + 1
            day.innerHTML += `<span></span>
                            <span></span>
                            <span></span>
                            <span></span>`
            if (i - first_day.getDay() + 1 === currDate.getDate() && year === currDate.getFullYear() && month === currDate.getMonth()) {
                day.classList.add('curr-date')
            }
        }
        calendar_days.appendChild(day)
    }
}

let month_list = calendar.querySelector('.month-list')

month_names.forEach((e, index) => {
    let month = document.createElement('div')
    month.innerHTML = `<div data-month="${index}">${e}</div>`
    month.querySelector('div').onclick = () => {
       ...