Minesweeper in 247 Bytes (by yui.dev)

HTML

Check out the blog post: https://yui.dev/blog/minesweeper-in-247-bytes

CSS

/* entirely optional, added for slightly better playability */
body {
  font-family: monospace;
  font-size: 1.5rem;
}
p {
  height: 30px;
  margin: 0;
}
p > a:not(:empty) {
  width: 25px;
  display: inline-block;
}

JavaScript

b=e=>document.body.innerHTML=m(73,e||[~9,..."1172711",~9].map(j=>m[i-=j]?++e:i).map(j=>b(b[i=j]^1|e),b[i]=!m[O--,i]*~e));b(m=t=>t--?`<a onmouseup=b(b[i=${t}]^=event.which)>${t%9?"*#F"[x=b[t]??=(O-=m[t]=Math.random()<.1,1)]??~x:"<p>"}`+m(t):O,O=64)