Writing Variables into HTML from Javascript

I have some javascript and HTML to display the BPM values of a keyboard tap. On the HTML at the bottom, i have some script to get the value of 'simpleTempo' form JAVASCRIPT and write it into a non editable text box however want this to be plain text which I can assign styles with CSS to. If you could help me - it would be really appreciated!

---------------------------JAVSCRIPT---------------------------

// JavaScript Document/* 

"use strict";


var startTime;
var beatTimes;
var xsum, xxsum, ysum, yysum, xysum;
var periodprev, aprev, bprev;
var isDone;

init();


function init() {
    startTime = null;
    beatTimes = [];
    xsum  = 0;
    xxsum = 0;
    ysum  = 0;
    yysum = 0;
    xysum = 0;
    isDone = false;
    document.onkeydown = doBeat;
}


function doBeat() {
    if (!isDone)
        countBeat(new Date().getTime());
    return true;
}


function countBeat(currTime) {
    // Coordinates for linear regression
    if (startTime == null)
        startTime = currTime;
    var x = beatTimes.length;
    var y = currTime - startTime;

    // Add beat
    beatTimes.push(y);
    var beatCount = beatTimes.length;
    setValue("simpleBeats", beatCount);
    setValue("simpleTime", floatToString(y / 1000, 3));

    // Regression cumulative variables
    xsum  += x;
    xxsum += x * x;
    ysum  += y;
    yysum += y * y;
    xysum += x * y;

    var tempo = 60000 * x / y;
    if (beatCount < 8 || tempo < 190)
        setValue("simplePosition", Math.floor(x / 4) + " : " + x % 4);
    else  // Two taps per beat
        setValue("simplePosition", Math.floor(x / 8) + " : " + Math.floor(x / 2) % 4 + "." + x % 2 * 5);

    if (beatCount >= 2) {
        // Period and tempo, simple
        var period = y / x;
        setValue("simpleTempo", floatToString(tempo, 2));
        setValue("simplePeriod", floatToString(period, 2));

        // Advanced
        var xx = beatCount * xxsum - xsum * xsum;
        var yy = beatCount * yysum - ysum * ysum;
        var xy = beatCount * xysum - xsum * ysum;
        var a = (beatCount * xysum - xsum * ysum) / xx;  // Slope
        var b = (ysum * xxsum - xsum * xysum) / xx;  // Intercept
        setValue("advancedPeriod", floatToString(a, 3));
        setValue("advancedOffset", floatToString(b, 3));
        setValue("advancedCorrelation", floatToString(xy * xy / (xx * yy), 9));
        setValue("advancedTempo", floatToString(60000 / a, 3));

        // Deviations from prediction
        if (beatCount >= 3) {
            setValue("simpleLastDev"  , floatToString(periodprev * x - y, 1));
            setValue("advancedStdDev" , floatToString(Math.sqrt(((yy - xy * xy / xx) / beatCount) / (beatCount - 2)), 3));
            setValue("advancedLastDev", floatToString(aprev * x + bprev - y, 1));
        }

        periodprev = period;
        aprev = a;
        bprev = b;
    }
}


function done() {
    isDone = true;
    setValue("simplePosition" , "");
    setValue("simpleLastDev"  , "");
    setValue("advancedLastDev", "");
}


// d: Number of decimal places
function floatToString(x, d) {
    if (x < 0)
        return "-" + floatToString(-x, d);
    var m = Math.pow(10, d);
    var tp = Math.round(x % 1 * m);
    var s = "";
    for (var i = 0; i < d; i++) {
        s = tp % 10 + s;
        tp = Math.floor(tp / 10);
    }
    return Math.floor(Math.round(x * m) / m) + "." + s;
}


function setValue(elemId, val) {
    document.getElementById(elemId).value = val;
}

---------------------------HTML---------------------------

        <form action="#" method="get" onsubmit="return false" onreset="init()">

<input id="simpleTempo" action="#" method="get"/>
<input id="simpleBeats" readonly="readonly" type="hidden" />
<input id="simplePosition" readonly="readonly" type="hidden"/>
<input id="simpleTime" readonly="readonly" type="hidden"/>
<input id="advancedStdDev" readonly="readonly" type="hidden"/>
<input id="advancedOffset" readonly="readonly" type="hidden"/>
<input id="advancedCorrelation" readonly="readonly" type="hidden"/>
<input id="simpleLastDev" readonly="readonly" type="hidden"/>
<input id="advancedLastDev" readonly="readonly" type="hidden"/>
<input id="simplePeriod" readonly="readonly" type="hidden"/>
<input id="advancedPeriod" readonly="readonly" type="hidden"/>
<input id="simpleTempo" readonly="readonly" type="hidden"/>

<input type="reset" alt="reset" class="imgClass"/>
</form>

<script type="application/javascript" src="tap-to-measure-tempo.js"></script>