* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

body {
    font-family: Arial, sans-serif;
    background: #111827;
    color: white;
    min-height: 100vh;
}

.app {
    max-width: 520px;
    margin: auto;
    padding: 18px;
}

.header {
    text-align: center;
    margin-bottom: 22px;
}

.header h1 {
    font-size: 25px;
    margin-bottom: 6px;
}

.header p {
    opacity: 0.75;
    font-size: 14px;
}

.menu {
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.btn {
    width: 100%;
    border: none;
    border-radius: 12px;
    padding: 15px 18px;

    font-size: 16px;
    font-weight: 700;

    color: white;
    cursor: pointer;

    transition:
        transform 0.12s ease,
        filter 0.12s ease;
}

/* BLUE */
.blue {
    background: #1976d2;
}

/* GREEN */
.green {
    background: #16a34a;
}

/* YELLOW */
.yellow {
    background: #d4a017;
    color: white;
}

/* RED */
.red {
    background: #dc2626;
}

/* CLICK EFFECT */
.btn:hover {
    filter: brightness(1.08);
}

.btn:active {
    transform: scale(0.96);
}

#content {
    margin-top: 20px;
}