body {
    margin: 0;
    padding: 0;
    font-family: "Comic Sans MS", "Arial", cursive;
    text-align: center;
    color: #222;

    /* Fondo tipo cuaderno */
    background:
        repeating-linear-gradient(
            to bottom,
            #ffffff,
            #ffffff 28px,
            #d7e3ff 29px
        );

    display: flex;
    flex-direction: column;
    align-items: center;
}

/* Título estilo pizarrón */
h2 {
    margin-top: 60px;
    font-size: 48px;
    font-weight: bold;
    color: #000;

    text-shadow: 2px 2px 0px #999;

    position: relative;
}

/* Detalle matemático */
h2::after {
    content: "  + 2x = ?";
    font-size: 24px;
    color: #444;
}

/* Caja estilo dibujo a mano */
.container {
    margin-top: 60px;
    padding: 40px 60px;

    background: #fff;

    border: 3px solid #000;
    border-radius: 12px;

    box-shadow: 6px 6px 0px #000;

    position: relative;
}

/* Stickman decorativo */
.container::before {
    content: "";
    position: absolute;
    left: -40px;
    bottom: -20px;
    width: 40px;
    height: 80px;
    background: none;
    border-left: 3px solid black;
    border-bottom: 3px solid black;
}

/* Botón estilo dibujado */
button {
    margin-top: 25px;
    padding: 12px 30px;
    font-size: 18px;
    font-family: inherit;
    color: #000;

    background: #fff;

    border: 3px solid #000;
    border-radius: 8px;

    cursor: pointer;
    font-weight: bold;

    box-shadow: 4px 4px 0px #000;

    transition: 0.1s ease;
}

button:hover {
    transform: rotate(-2deg) scale(1.05);
}

button:active {
    transform: translateY(3px);
    box-shadow: 2px 2px 0px #000;
}

/* Botón de regreso */
.back-btn {
    margin: 40px 0 60px 0;
    padding: 12px 30px;
    font-size: 18px;
    font-family: inherit;
    color: #000;

    background: #f5f5f5;

    border: 3px dashed #000;
    border-radius: 8px;

    cursor: pointer;
    font-weight: bold;

    box-shadow: 4px 4px 0px #000;

    transition: 0.1s ease;
}

.back-btn:hover {
    transform: rotate(2deg) scale(1.05);
}