style.css

body {
  width: 100%;
  height: max-content;
  min-height: fit-content;
  margin: 0;
  padding: 0;
  overflow-x: hidden;
}

.puzzle-container {
  background: black;
  display: inline-block;
  padding: 0;
  background-color: white;
  width: fit-content;
  max-width: fit-content !important;

}

#puzzle {
  background-color: black;
  width: fit-content;
  display: grid;
}

#puzzle.special {
  zoom: 2;
}

.puzzle-border {
  border: 1.75em solid black;
}

.cell-container {
  position: relative;
}

.cell {
  justify-content: center;
  align-items: center;
  display: flex;
  font-family: Arial, Helvetica, sans-serif;
  font-weight: bold;
  background: black;
  text-align: center;
  border: .01em solid black;
  /* SIZING */
  width: 100%;
  height: 100%;
  padding: 0;
}

.cell.active {
  background: white;
  text-transform: lowercase;
}

.cell.active:focus {
  background-color: rgba(25,85,165,.9);
  color: white;
}

.cell.active:focus + span {
  color: white;
}

.cell:focus {
  background-color: rgb(228, 228, 228);
  border: none;
  outline: none;
}

button {
  margin: 50px;
}

#generate, #check, #solution, #reset {
  margin: 0 3px;
}

#generate {
  margin-left: 5px;
}

.dropdown-menu .dropdown-item:hover {
  cursor: pointer;
}

.puzzleButtons {
  margin: .75em .3em;
  margin-left: 0;
}

.puzzleButtons > button {
  font-size: .85em;
  text-align: center;
  vertical-align: middle;
}

input[type="text"] {
  font-size: 1em;
}

#across, #down {
  margin-right: 10px;
}

#down {
  margin-right: 10px; 
}

#hints {
  padding: .1vmax;
  margin-left: .2em;
  margin-right: .5em;
}

.highlight {
  background: #FFC107;
  color: black;
}

.puzzle-label {
  font-size: .5em;
  position: absolute;
  top: 0.000001%;
  left: 9.2%;
  z-index: 10;
  color: black;
}

/* OVERLAY */

@keyframes fadeIn {
  0% { opacity: 0; }
  100% { opacity: 1 }
}

@keyframes fadeOut {
  0% { opacity: 1 }
  100% { opacity: 0 }
}

.overlay {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background: linear-gradient(#0007, #0000), #123;
  margin: 0;
  overflow: hidden;
}

.fade-in {
  animation: fadeIn 0.7s ease-in;
}

.fade-out {
  animation: fadeOut 0.7s ease-in;
}

@keyframes firework {
  0% { transform: translate(var(--x), var(--initialY)); width: var(--initialSize); opacity: 1; }
  50% { width: 0.5vmin; opacity: 1; }
  100% { width: var(--finalSize); opacity: 0; }
}

.firework,
.firework::before,
.firework::after
{
  --initialSize: 0.5vmin;
  --finalSize: 45vmin;
  --particleSize: 0.2vmin;
  --color1: yellow;
  --color2: khaki;
  --color3: white;
  --color4: lime;
  --color5: gold;
  --color6: mediumseagreen;
  --y: -30vmin;
  --x: -50%;
  --initialY: 60vmin;
  content: "";
  animation: firework 2s infinite;
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, var(--y));
  width: var(--initialSize);
  aspect-ratio: 1;
  background: 
    /*
    radial-gradient(circle, var(--color1) var(--particleSize), #0000 0) 0% 0%,
    radial-gradient(circle, var(--color1) var(--particleSize), #0000 0) 100% 0%,
    radial-gradient(circle, var(--color1) var(--particleSize), #0000 0) 100% 100%,
    radial-gradient(circle, var(--color1) var(--particleSize), #0000 0) 0% 100%,
    */
    
    radial-gradient(circle, var(--color1) var(--particleSize), #0000 0) 50% 0%,
    radial-gradient(circle, var(--color2) var(--particleSize), #0000 0) 100% 50%,
    radial-gradient(circle, var(--color3) var(--particleSize), #0000 0) 50% 100%,
    radial-gradient(circle, var(--color4) var(--particleSize), #0000 0) 0% 50%,
    
    /* bottom right */
    radial-gradient(circle, var(--color5) var(--particleSize), #0000 0) 80% 90%,
    radial-gradient(circle, var(--color6) var(--particleSize), #0000 0) 95% 90%,
    radial-gradient(circle, var(--color1) var(--particleSize), #0000 0) 90% 70%,
    radial-gradient(circle, var(--color2) var(--particleSize), #0000 0) 100% 60%,
    radial-gradient(circle, var(--color3) var(--particleSize), #0000 0) 55% 80%,
    radial-gradient(circle, var(--color4) var(--particleSize), #0000 0) 70% 77%,
    
    /* bottom left */
    radial-gradient(circle, var(--color5) var(--particleSize), #0000 0) 22% 90%,
    radial-gradient(circle, var(--color6) var(--particleSize), #0000 0) 45% 90%,
    radial-gradient(circle, var(--color1) var(--particleSize), #0000 0) 33% 70%,
    radial-gradient(circle, var(--color2) var(--particleSize), #0000 0) 10% 60%,
    radial-gradient(circle, var(--color3) var(--particleSize), #0000 0) 31% 80%,
    radial-gradient(circle, var(--color4) var(--particleSize), #0000 0) 28% 77%,
    radial-gradient(circle, var(--color5) var(--particleSize), #0000 0) 13% 72%,
    
    /* top left */
    radial-gradient(circle, var(--color6) var(--particleSize), #0000 0) 80% 10%,
    radial-gradient(circle, var(--color1) var(--particleSize), #0000 0) 95% 14%,
    radial-gradient(circle, var(--color2) var(--particleSize), #0000 0) 90% 23%,
    radial-gradient(circle, var(--color3) var(--particleSize), #0000 0) 100% 43%,
    radial-gradient(circle, var(--color4) var(--particleSize), #0000 0) 85% 27%,
    radial-gradient(circle, var(--color5) var(--particleSize), #0000 0) 77% 37%,
    radial-gradient(circle, var(--color6) var(--particleSize), #0000 0) 60% 7%,
    
    /* top right */
    radial-gradient(circle, var(--color1) var(--particleSize), #0000 0) 22% 14%,
    radial-gradient(circle, var(--color1) var(--particleSize), #0000 0) 45% 20%,
    radial-gradient(circle, var(--color1) var(--particleSize), #0000 0) 33% 34%,
    radial-gradient(circle, var(--color1) var(--particleSize), #0000 0) 10% 29%,
    radial-gradient(circle, var(--color1) var(--particleSize), #0000 0) 31% 37%,
    radial-gradient(circle, var(--color1) var(--particleSize), #0000 0) 28% 7%,
    radial-gradient(circle, var(--color1) var(--particleSize), #0000 0) 13% 42%
    ;
  background-size: var(--initialSize) var(--initialSize);
  background-repeat: no-repeat;
}

.firework::before {
  --x: -50%;
  --y: -50%;
  --initialY: -50%;
/*   transform: translate(-20vmin, -2vmin) rotate(40deg) scale(1.3) rotateY(40deg); */
  transform: translate(-50%, -50%) rotate(40deg) scale(1.3) rotateY(40deg);
/*   animation: fireworkPseudo 2s infinite; */
}

.firework::after {
  --x: -50%;
  --y: -50%;
  --initialY: -50%;
/*   transform: translate(44vmin, -50%) rotate(170deg) scale(1.15) rotateY(-30deg); */
  transform: translate(-50%, -50%) rotate(170deg) scale(1.15) rotateY(-30deg);
/*   animation: fireworkPseudo 2s infinite; */
}

.firework:nth-child(2) {
  --x: 30vmin;
}

.firework:nth-child(2),
.firework:nth-child(2)::before,
.firework:nth-child(2)::after {
  --color1: pink;
  --color2: violet;
  --color3: fuchsia;
  --color4: orchid;
  --color5: plum;
  --color6: lavender;  
  --finalSize: 40vmin;
  left: 30%;
  top: 60%;
  animation-delay: -0.25s;
}

.firework:nth-child(3) {
  --x: -30vmin;
  --y: -50vmin;
}

.firework:nth-child(3),
.firework:nth-child(3)::before,
.firework:nth-child(3)::after {
  --color1: cyan;
  --color2: lightcyan;
  --color3: lightblue;
  --color4: PaleTurquoise;
  --color5: SkyBlue;
  --color6: lavender;
  --finalSize: 35vmin;
  left: 70%;
  top: 60%;
  animation-delay: -0.4s;
}