style.css

:root {
    --dark-blue: #1C274C;
}

* {
    margin: 0;
    padding: 0;
    font-family: Arial, Helvetica, sans-serif;
    color: var(--dark-blue);
}

body {
    height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    background-color: #8EC5FC;
    background-image: linear-gradient(62deg, #8EC5FC 0%, #E0C3FC 100%);
}

#game-container {
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
}

#volume {
    width: 40px;
    position: absolute;
    top: 0;
    right: 0;
    margin: 15px;
    cursor: pointer;
}

#resetBtn {
    margin: 10px;
    padding: 5px 10px;
    border: 1px solid var(--dark-blue);
    border-radius: 5px;
    background-color: #caaffc;
    font-size: large;
    transition: 0.2s;
}

#resetBtn:hover {
    background-color: #d4bfff;
    border-color: #caaffc;
    cursor: pointer;
}

#stats {
    display: flex;
    justify-content: space-evenly;
    width: 100%;
}

#cards-container {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    grid-template-rows: repeat(4, 1fr);
    grid-gap: 10px;
    margin: 10px 0;
}

.card {
    /* center card images */
    display: flex;
    justify-content: center;
    align-items: center;

    /* mobile width */
    width: 20vw;
    height: 20vw; 

    /* desktop width */
    max-width: 100px;
    max-height: 100px;

    border: 1px solid #ccc;
    border-radius: 10px;
    transition: transform 0.6s; /* Smooth flip animation */
    cursor: pointer;

    background-image: url(images/card-back.png);
    background-repeat: no-repeat;
    background-size: cover;
    background-position: center;
}

.card img {
    width: 15vw; /* mobile */
    max-width: 80px; /* desktop */
    visibility: hidden;
}

.flipped {
    transform: rotateY(180deg);
    background: none;
    background-color: white;
}

.flipped img {
    visibility: visible;
}

.matched {
    border: 0px;
    background: none;
}