index.css

:root {
  --radius: 5px;
  --main-frame: 15px solid white;
}

* {
    box-sizing: border-box;
}

html, body {
    margin: 0;
    padding: 0;
}

body {
    background-image: url('/xmas-bg3.png');
    background-size: cover;
    display: flex;
    height: 100vh;
    align-items: center;
}

h1 {
    font-family: 'Poppins', sans-serif;
}

main {
    display: flex;
    margin: 0 auto;
    position: relative;
    padding: 0;
}

img {
    height: 450px;
    display: block;
}

.left-door {
    border: var(--main-frame);
    border-right: 0;
    border-top-left-radius: var(--radius);
    border-bottom-left-radius: var(--radius);
}

.left-door img {
    border-right: 0;
    border-top-left-radius: var(--radius);
    border-bottom-left-radius: var(--radius);
}

.right-door {
    border: var(--main-frame);
    border-left: 0;
    border-top-right-radius: var(--radius);
    border-bottom-right-radius: var(--radius);
}

.right-door img {
    border-left: 0;
    border-top-right-radius: var(--radius);
    border-bottom-right-radius: var(--radius);
}

.joke-display {
    position: absolute;
    background-color: white;
    opacity: 0;
    left: 0; 
    right: 0; 
    display: flex;
    align-items: center;
    justify-content: center;
    text-align: center;
    border: var(--main-frame);
    height: 100%;
    padding: 1em;
    cursor: pointer;
}

/* animation */

@keyframes display-joke {
  from {opacity: 0;}
  to {opacity: 1;}
}

@keyframes left-open {
  0% {
        transform: translateX(0%);
      }
  100% {
        transform: translateX(-100%);
      }
}

@keyframes right-open {
  from {
        transform: translateX(0%);
      }
  to {
        transform: translateX(100%);
      }
}