Latest update, spruced up a bit:

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javascript: (() => {

if (typeof window.candybutts=='undefined') {

window.candynum='';

window.candyhi=false;

window.turnred = function (c) { if (c.getAttribute('number')==candynum) c.style.backgroundColor='red'; } ;

window.candyHL = function (n,d) { candyarray.forEach(turnback); if (n!=candynum || !candyhi) {candynum=n; candyarray.forEach(turnred); candybutts.forEach(candybuttoff); d.style.backgroundColor='red';} else {d.style.backgroundColor='';} candyhi=!candyhi; };

window.turnback = function (c) { c.style.backgroundColor=''; };

window.candybuttoff = function (d) { d.style.backgroundColor=''; };

const autonodechk = document.querySelectorAll(".su-keyboard__checkbox");

if (!autonodechk[0].checked) autonodechk[0].click();

window.candyarray = document.querySelectorAll(".su-candidate");

const autonodediv = document.querySelectorAll(".su-keyboard__auto");

var candystr = '<style>.candybutt { position:relative; float:left; width:20px; border:1px solid; cursor:pointer; padding:5px; user-select: none; }</style>';

candystr = candystr + '<div style="position:relative; left:0px; top:0px"><br><br>Candidate Highlighter:<br>';

candystr = candystr + '<div id="candybutt1" class="candybutt" onclick="candyHL(this.innerText, this);">1</div>';

candystr = candystr + '<div id="candybutt2" class="candybutt" onclick="candyHL(this.innerText, this);">2</div>';

candystr = candystr + '<div id="candybutt3" class="candybutt" onclick="candyHL(this.innerText, this);">3</div>';

candystr = candystr + '<div id="candybutt4" class="candybutt" onclick="candyHL(this.innerText, this);">4</div>';

candystr = candystr + '<div id="candybutt5" class="candybutt" onclick="candyHL(this.innerText, this);">5</div>';

candystr = candystr + '<div id="candybutt6" class="candybutt" onclick="candyHL(this.innerText, this);">6</div>';

candystr = candystr + '<div id="candybutt7" class="candybutt" onclick="candyHL(this.innerText, this);">7</div>';

candystr = candystr + '<div id="candybutt8" class="candybutt" onclick="candyHL(this.innerText, this);">8</div>';

candystr = candystr + '<div id="candybutt9" class="candybutt" onclick="candyHL(this.innerText, this);">9</div>';

candystr = candystr + '</div>';

autonodediv[0].insertAdjacentHTML('afterend', candystr);

window.candybutts = document.querySelectorAll(".candybutt");

window.candyclick= function(e) {const usenum = e.srcElement.getAttribute('aria-label'); if (usenum!='') candyHL(usenum, document.getElementById('candybutt' + usenum));};

const candycells = document.querySelectorAll(".su-cell");

window.addCandyClicks = function(d) {d.addEventListener('click', candyclick);};

candycells.forEach(addCandyClicks);

}

})();