Heatmap

<div class="viz">
  <svg id="svg"></svg>
  <div class="scale minor" id="scale"><span>0</span><i></i><span>100</span></div>
</div>

body{display:block}
.viz{display:flex;flex-direction:column;width:100%;height:100%}
svg{flex:1;min-height:0;display:block;width:100%;overflow:visible}
.scale{flex:none;display:flex;align-items:center;justify-content:center;gap:6px;padding:2px 4px 4px;font:600 9px/1 system-ui,sans-serif;color:var(--muted)}
.scale i{width:60px;height:7px;border-radius:4px;background:linear-gradient(90deg, color-mix(in srgb, var(--accent) 12%, var(--surface)), var(--accent))}
.cell{transition:fill .6s ease}

var svg = document.getElementById('svg');
var NS = 'http://www.w3.org/2000/svg';
function se(t){ return document.createElementNS(NS,t); }
function sa(e,o){ for (var k in o) e.setAttribute(k,o[k]); }
function R(a,b){ return a + Math.random()*(b-a); }

var COLS = 8, ROWS = 4;
var cells = [];
for (var r=0;r<ROWS;r++) for (var c=0;c<COLS;c++) cells.push({ r:r, c:c, v:R(10,90) });
var W=300, H=200;
var rects = [];

function measure(){
  var rc = svg.getBoundingClientRect();
  W = Math.max(rc.width,10); H = Math.max(rc.height,10);
  sa(svg,{ viewBox: '0 0 ' + W + ' ' + H });
}

function build(){
  svg.innerHTML = '';
  rects = [];
  var padL=8, padR=8, padT=8, padB=8;
  var pw=W-padL-padR, ph=H-padT-padB;
  var gap=2;
  var cw=(pw-gap*(COLS-1))/COLS, ch=(ph-gap*(ROWS-1))/ROWS;
  cells.forEach(function(cell){
    var x = padL+cell.c*(cw+gap), y = padT+cell.r*(ch+gap);
    var rect = se('rect');
    sa(rect,{x:x,y:y,width:cw,height:ch,rx:2,class:'cell'});
    svg.appendChild(rect);
    rects.push(rect);
  });
  paint();
}

function paint(){
  cells.forEach(function(cell,i){
    var pct = Math.max(6,Math.min(96, cell.v));
    rects[i].setAttribute('fill', 'color-mix(in srgb, var(--accent) ' + pct + '%, var(--surface))');
  });
}

new ResizeObserver(function(){ measure(); build(); }).observe(svg);
measure();
build();
setInterval(function(){
  cells.forEach(function(cell){ cell.v = R(8,92); });
  paint();
}, 2800);