:root {
    /* Colors */
    --color-background: #e9f5e1;
    --color-text: #333;
    --color-header-bg: #88c070;
    --color-header-text: #ffffff;
    --color-card-bg: #66a15a;
    --color-card-border: #4d8044;
    --color-card-flipped-bg: #ffffff;
    --color-card-flipped-text: #4d8044;
    --color-button-bg: #4d8044;
    --color-button-hover-bg: #88c070;
    --color-button-text: #ffffff;

    /* Fonts */
    --font-family-body: Arial, sans-serif;
    --font-size-base: 16px;
    --font-size-large: 24px;

    /* Dimensions */
    --card-size: 100px;
    --animation-speed: 0.3s;
    --grid-max-width: 600px;
}

body {
    font-family: var(--font-family-body);
    margin: 0;
    padding: 0;
    text-align: center;
    background-color: var(--color-background);
    color: var(--color-text);
}

.header {
    padding: 20px;
    background-color: var(--color-header-bg);
    color: var(--color-header-text);
}

.header__title {
    margin: 0;
}

.header__description {
    margin: 10px 0 0;
}

.main {
    display: flex;
    flex-direction: column;
    align-items: center;
    padding: 20px;
}

.game-board {
    display: grid;
    gap: 10px;
    max-width: var(--grid-max-width);
    margin: 20px auto;
    grid-template-columns: repeat(auto-fit, minmax(var(--card-size), 1fr));
}

.game-board__card {
    width: var(--card-size);
    height: var(--card-size);
    background-color: var(--color-card-bg);
    border: 2px solid var(--color-card-border);
    border-radius: 8px;
    cursor: pointer;
    display: flex;
    justify-content: center;
    align-items: center;
    font-size: 0;
    transition: transform var(--animation-speed) ease, background-color var(--animation-speed);
}

.game-board__card--flipped,
.game-board__card--matched {
    background-color: var(--color-card-flipped-bg);
    font-size: var(--font-size-large);
    font-weight: bold;
    color: var(--color-card-flipped-text);
    transform: scale(1.05);
}

.game-board__card--disabled {
    pointer-events: none;
    cursor: default;
}

.scoreboard {
    margin-top: 20px;
}

.scoreboard__difficulty {
    margin-bottom: 10px;
}

.scoreboard__difficulty select {
    padding: 5px;
}

.scoreboard__reset-button {
    padding: 10px 20px;
    background-color: var(--color-button-bg);
    color: var(--color-button-text);
    border: none;
    border-radius: 4px;
    cursor: pointer;
    font-size: var(--font-size-base);
    transition: background-color var(--animation-speed);
}

.scoreboard__reset-button:hover {
    background-color: var(--color-button-hover-bg);
}

.scoreboard__timer {
    margin: 10px 0;
    font-size: var(--font-size-base);
    font-weight: bold;
}