JSFiddle - React, Tailwind, and code Playground

HTML

<div class="row">
		<div class="calculator-2">
			<div class="row">
				<p class="calculator-p" style="margin:8px;">Ваша дата рождения</p>			
				<div class="select-box-2">
					<select class="form-control pink-select" id="days">
							<option value="01">01</option>
							<option value="02">02</option>
							<option value="03">03</option>
							<option value="04">04</option>
							<option value="05">05</option>
							<option value="06">06</option>
							<option value="07">07</option>
							<option value="08">08</option>
							<option value="09">09</option>
							<option value="10">10</option>
							<option value="11">11</option>
							<option value="12">12</option>
							<option value="13">13</option>
							<option value="14">14</option>
							<option value="15">15</option>
							<option value="16">16</option>
							<option value="17">17</option>
							<option value="18">18</option>
							<option value="19">19</option>
							<option value="20">20</option>
							<option value="21">21</option>
							<option value="22">22</option>
							<option value="23">23</option>
							<option value="24">24</option>
							<option value="25">25</option>
							<option value="26">26</option>
							<option value="27">27</option>
							<option value="28">28</option>
							<option value="29">29</option>
							<option value="30">30</option>
							<option value="31">31</option>
					</select>	
					 <select class="form-control pink-select" id="months">
							<option value="January">Январь</option>
							<option value="February" selected>Февраль</option>
							<option value="March">Март</option>
							<option value="April">Апрель</option>
							<option value="May">Май</option>
							<option value="June">Июнь</option>
							<option value="July">Июль</option>
							<option value="August">Август</option>
							<option value="September">Сентябрь</option>
							<option value="October">Октябрь</option>
							<option...

CSS

body{
    width: 400px;
    margin: 0 auto;
	background: #E5E7DF;
}
#go-pif {
    background: rgba(23, 40, 40, 0.68);
    width: 205px;

    padding: 10px;
    cursor: pointer;
    margin-top: 10px;
    display: inline-block;

    color: white;
}
.row {
	margin-top: 10px;
    text-align: center;
}

JavaScript

// Пифагор начало

	function pifagor(pifag) {
		var massiv = [];
		massiv[0] = ((pifag.getDate() - (pifag.getDate() % 10)) / 10);
		massiv[1] = (pifag.getDate() % 10);
		
		var f_month = pifag.getMonth() + 1;
		massiv[2] = ((f_month - (f_month % 10)) / 10);
		massiv[3] = (f_month % 10);
		
		massiv[4] = ((pifag.getFullYear() - (pifag.getFullYear() % 1000)) / 1000);
		massiv[5] = (((pifag.getFullYear() - (massiv[4] * 1000)) - (pifag.getFullYear() % 100)) / 100);
		massiv[6] = (((pifag.getFullYear() - (massiv[4] * 1000) - (massiv[5] * 100)) - (pifag.getFullYear() % 10)) / 10);
		massiv[7] = (pifag.getFullYear() % 10);
		
		var rch1 = massiv[0] + massiv[1] + massiv[2] + massiv[3] + massiv[4] + massiv[5] + massiv[6] + massiv[7];
		var rch2 = (rch1 % 10) + ((rch1 - (rch1 % 10)) / 10);
		
		if (massiv[0] > 0) { 
			var rch3 = rch1 - (massiv[0] * 2); 
		}
		else if (massiv[0] == 0) {
			var rch3 = rch1 - (massiv[1] * 2);
		}
		
		var rch4 = (rch3 % 10) + ((rch3 - (rch3 % 10)) / 10);
		
		massiv[8] = ((rch1 - (rch1 % 10)) / 10);
		massiv[9] = (rch1 % 10);
		massiv[10] = ((rch2 - (rch2 % 10)) / 10);
		massiv[11] = (rch2 % 10);
		massiv[12] = ((rch3 - (rch3 % 10)) / 10);
		massiv[13] = (rch3 % 10);
		massiv[14] = ((rch4 - (rch4 % 10)) / 10);
		massiv[15] = (rch4 % 10);
		
		var rch5 = rch1 + rch3;
		var rch6 = rch2 + rch4;
		
		var fkol_10 = 0;
		var fkol_11 = 0;
		var fkol_12 = 0;
 		var fkol_1sum = '';
		var fkol_2sum = '';
		var fkol_3sum = '';
		var fkol_4sum = '';
		
		//инициализируем массив
		var fkol = [];
		for (var i = 0; i < 10; i++) {
			fkol[i] = 0;
		}
		
		
		var i = 0;
		var j = 0;
		
		function splitNumber(number) {
    //убрал добавление скобок для удобства поиска
			number.toString().split('').forEach(number => massiv.push(number));
		}
		splitNumber(rch5);
		splitNumber(rch6);	
		

		while (i <= 19) {
    	//так как в нашем массиве мы учитываем только цифры от 1 до 9, то нужен иф
    	if (i < 10) {
				fkol[massiv[i]]++;
      }
			
			if ((rch1 == 10...