HTML, CSS and JavaScript playground

.heart-beat {
  position: relative;
  display: grid;
  grid-template-columns: repeat(9, 1fr);
  grid-template-rows: repeat(8, 1fr);
  grid-template-areas:
    "a1 a2 a3 a4 a5 a6 a7 a8 a9"
    "b1 b2 b3 b4 b5 b6 b7 b8 b9"
    "c1 c2 c3 c4 c5 c6 c7 c8 c9"
    "d1 d2 d3 d4 d5 d6 d7 d8 d9"
    "e1 e2 e3 e4 e5 e6 e7 e8 e9"
    "f1 f2 f3 f4 f5 f6 f7 f8 f9"
    "g1 g2 g3 g4 g5 g6 g7 g8 g9"
    "h1 h2 h3 h4 h5 h6 h7 h8 h9";
  margin: auto;
  width: 302px;
  background: black;
  color: #fff;
  gap: 4px;

border-top: 66px solid #000;
  border-bottom: 66px solid #000;
  border-right: 49px solid #000;
  border-left: 49px solid #000;

}

.heart-beat p {
  margin: 0;
  aspect-ratio: 1 / 1;
  background: red;
  display: flex;
  align-items: center;
  justify-content: center;
}

.heart-beat p:nth-child(1),
.heart-beat p:nth-child(2),
.heart-beat p:nth-child(3),
.heart-beat p:nth-child(4),
.heart-beat p:nth-child(5),
.heart-beat p:nth-child(8),
.heart-beat p:nth-child(9),
.heart-beat p:nth-child(12),
.heart-beat p:nth-child(13),
.heart-beat p:nth-child(17),
.heart-beat p:nth-child(21),
.heart-beat p:nth-child(22),
.heart-beat p:nth-child(30),
.heart-beat p:nth-child(31),
.heart-beat p:nth-child(37),
.heart-beat p:nth-child(38),
.heart-beat p:nth-child(42),
.heart-beat p:nth-child(43),
.heart-beat p:nth-child(45),
.heart-beat p:nth-child(46) {
  background: green;
}

.heart-beat p:nth-child(1) {
  grid-area: a2;
}

.heart-beat p:nth-child(2) {
  grid-area: a3;
}

.heart-beat p:nth-child(3) {
  grid-area: a7;
}

.heart-beat p:nth-child(4) {
  grid-area: a8;
}

.heart-beat p:nth-child(5) {
  grid-area: b1;
}

.heart-beat p:nth-child(6) {
  grid-area: b2;
}

.heart-beat p:nth-child(7) {
  grid-area: b3;
}

.heart-beat p:nth-child(8) {
  grid-area: b4;
}

.heart-beat p:nth-child(9) {
  grid-area: b6;
}

.heart-beat p:nth-child(10) {
  grid-area: b7;
}

.heart-beat p:nth-child(11) {
  grid-area: b8;
}

.heart-beat p:nth-child(12) {
  grid-area: b9;
}

.heart-beat p:nth-child(13) {
  grid-area: c1;
}

.heart-beat p:nth-child(14) {
  grid-area: c2;
}

.heart-beat p:nth-child(15) {
  grid-area: c3;
}

.heart-beat p:nth-child(16) {
  grid-area: c4;
}

.heart-beat p:nth-child(17) {
  grid-area: c5;
}

.heart-beat p:nth-child(18) {
  grid-area: c6;
}

.heart-beat p:nth-child(19) {
  grid-area: c7;
}

.heart-beat p:nth-child(20) {
  grid-area: c8;
}

.heart-beat p:nth-child(21) {
  grid-area: c9;
}

.heart-beat p:nth-child(22) {
  grid-area: d1;
}

.heart-beat p:nth-child(23) {
  grid-area: d2;
}

.heart-beat p:nth-child(24) {
  grid-area: d3;
}

.heart-beat p:nth-child(25) {
  grid-area: d4;
}

.heart-beat p:nth-child(26) {
  grid-area: d5;
}

.heart-beat p:nth-child(27) {
  grid-area: d6;
}

.heart-beat p:nth-child(28) {
  grid-area: d7;
}

.heart-beat p:nth-child(29) {
  grid-area: d8;
}

.heart-beat p:nth-child(30) {
  grid-area: d9;
}

.heart-beat p:nth-child(31) {
  grid-area: e2;
}

.heart-beat p:nth-child(32) {
  grid-area: e3;
}

.heart-beat p:nth-child(33) {
  grid-area: e4;
}

.heart-beat p:nth-child(34) {
  grid-area: e5;
}

.heart-beat p:nth-child(35) {
  grid-area: e6;
}

.heart-beat p:nth-child(36) {
  grid-area: e7;
}

.heart-beat p:nth-child(37) {
  grid-area: e8;
}

.heart-beat p:nth-child(38) {
  grid-area: f3;
}

.heart-beat p:nth-child(39) {
  grid-area: f4;
}

.heart-beat p:nth-child(40) {
  grid-area: f5;
}

.heart-beat p:nth-child(41) {
  grid-area: f6;
}

.heart-beat p:nth-child(42) {
  grid-area: f7;
}

.heart-beat p:nth-child(43) {
  grid-area: g4;
}

.heart-beat p:nth-child(44) {
  grid-area: g5;
}

.heart-beat p:nth-child(45) {
  grid-area: g6;
}

.heart-beat p:nth-child(46) {
  grid-area: h5;
}