board.css

html { font-size: 2vmin; } 
/* Responsive/Fluid Fonts
https://www.smashingmagazine.com/2016/05/fluid-typography/
*/
h1 { 
  font-size: 2rem; 
  text-align: center; 
}


.game-table {
  display: grid;
  grid-template: 5vmin auto 5vmin / 5vmin auto 5vmin;
  justify-content: center;
}

/* CSS Grid of 15 * 15 
https://css-tricks.com/snippets/css/complete-guide-grid/#prop-grid-column-row
 */
.game-board{ 
    grid-column: 2 / 3; /* This grid is itself inside another parent grid. So it's second-row, second-column in parent layout */
    display: grid;
     /* vmins instead of px helps to make the grid resize itself based on the screen size */
    grid-template-columns: repeat(15, 5vmin);
    grid-template-rows: repeat(15, 5vmin);
    justify-content: center;
    align-content: center;
    box-sizing: border-box;
    margin: 0.5vmin;
   }

.box, .green, .yellow, .blue, .red {
    position: relative;
    border: 1px solid black;
    height: 5vmin;
    width: 5vmin;
    line-height: 5vmin;
    font-size: 3.5vmin; 
    text-align: center;
    box-sizing: border-box;
}   


.green-home{
    position: relative;
    background-color: white;
    width: 30vmin;
    height: 30vmin;
    box-shadow: 0 0 0 1px black; /* Real Border*/
    border: 5vmin solid limegreen; /* Inner square or Inner Border :-) */
    box-sizing: border-box;

    /* 4 circles as background */
    background: 
    radial-gradient(circle at 25% 25%,limegreen 3vmin, transparent 0),
    radial-gradient(circle at 25% 75%,limegreen 3vmin, transparent 0),
    radial-gradient(circle at 75% 25%,limegreen 3vmin, transparent 0),
    radial-gradient(circle at 75% 75%,limegreen 3vmin, transparent 0); 
    
    grid-column-start: 1;
    grid-column-end: 7;
    grid-row-start: 1;
    grid-row-end: 7;
}
.green{background-color: limegreen;}

.yellow-home{
  background-color: white;
  width: 30vmin;
  height: 30vmin;
  box-shadow: 0 0 0 1px black;
  border: 5vmin solid yellow;
  box-sizing: border-box;

  background: 
    radial-gradient(circle at 25% 25%,yellow 3vmin, transparent 0),
    radial-gradient(circle at 25% 75%,yellow 3vmin, transparent 0),
    radial-gradient(circle at 75% 25%,yellow 3vmin, transparent 0),
    radial-gradient(circle at 75% 75%,yellow 3vmin, transparent 0);

  grid-column-start: 10;
  grid-column-end: -1; /* can also write - span 6 */
  grid-row-start: 1;
  grid-row-end: 7;
}
.yellow{background-color: yellow;}

.blue-home{
  background-color: white;
  width: 30vmin;
  height: 30vmin;
  box-shadow: 0 0 0 1px black;
  border: 5vmin solid blue;
  box-sizing: border-box;

  background: 
    radial-gradient(circle at 25% 25%,blue 3vmin, transparent 0),
    radial-gradient(circle at 25% 75%,blue 3vmin, transparent 0),
    radial-gradient(circle at 75% 25%,blue 3vmin, transparent 0),
    radial-gradient(circle at 75% 75%,blue 3vmin, transparent 0);

  grid-column-start: 10;
  grid-column-end: -1;
  grid-row-start: 10;
  grid-row-end: -1;
} 
.blue{background-color: blue;}

.red-home{
  position: relative;
  background-color: white;
  width: 30vmin; 
  height: 30vmin;
  box-shadow: 0 0 0 1px black;
  border: 5vmin solid red;
  box-sizing: border-box;

  background: 
    radial-gradient(circle at 25% 25%,red 3vmin, transparent 0),
    radial-gradient(circle at 25% 75%,red 3vmin, transparent 0),
    radial-gradient(circle at 75% 25%,red 3vmin, transparent 0),
    radial-gradient(circle at 75% 75%,red 3vmin, transparent 0);

  grid-column-start: 1;
  grid-column-end: 7; 
  grid-row-start: 10;
  grid-row-end: -1; 
}
.red{background-color: red;}

.home{
    position: relative;
    grid-column-start: 7;
    grid-column-end: 10;
    grid-row-start: 7;
    grid-row-end: 10;   
    border: 1px solid black;
    box-sizing: border-box; 

    /* Finally figured out how to make all the 4 triangles using just a single line.
     Took lot of digging and reading of various types of gradients. 
     Thanks MDN Web Docs for immense help. Pie chart example did the trick
     https://developer.mozilla.org/en-US/docs/Web/CSS/conic-gradient */
    background: 
    conic-gradient(
      from -45deg, 
    yellow 90deg,
    blue 90deg 180deg, 
    red 180deg 270deg,
    limegreen 270deg 360deg
     );
}

.yellow-player{
  grid-column: 1 / 4;
  line-height: 7vmin;
  vertical-align: bottom;
  font-size: 1.2rem;
  font-weight: bold;
  transform: rotate(180deg);
  transform-origin: center;
  padding-left: 6vmin;
}
.blue-player{
  display: flex;
  grid-column: 3 / 4;
  font-size: 1.2rem;
  font-weight: bold;
  align-items: flex-end;
}
.blue-player-name{
  display: block;
  transform: rotate(-90deg);
  transform-origin: top left;
  white-space: nowrap;
}
.red-player{
  grid-column: 1 /4;
  font-size: 1.2rem;
  font-weight: bold;
  padding-left: 5.5vmin;
}
.green-player{
  grid-column: 1 / 2;
  font-size: 1.2rem;
  font-weight: bold;
  white-space: nowrap;
  transform: rotate(90deg);
  transform-origin: top right;
  padding-left: 5vmin;
}