#cuerpo {width: 99%;
        background: #33FFFF;
        font-size: 23px;
}
article {color: #000000;
        display: inline-block;
        font-size: 25px;
        text-align: center;
        margin-bottom: 10px;
        margin-left: 50px;
}
#Explicación { text-align: center;
            width: 87%;
            height: 50px;
            display: inline-block;
            color:#000000;
            font-size: 40px;
 }
#Actividad { text-align: left;
            width: 87%;
            height: 550px;
            display: block;
            margin-top: 0px;
 }
 #columna {width: 12%;
    height: 503px;
    text-align: center;
    display: inline-block;
    float: right;
}
#Siguiente { 
    border-radius: 10px;
    padding-bottom: initial;
    color: #0033FF;
    background-color: FFFFFF;
    width: 120px;
    height: 100px;
    margin: 20px 0px;
    font-size: 25px;
}#Principal {
  border-radius: 10px;
    padding-bottom: initial;
    color: #FFFFFF;
    background-color: red;
    width: 120px;
    height: 50px;
    margin: 30px auto;
    font-size: 20px;  
}#lasvidas{
        margin: 10px 30px;
        font-size: 35px;
        color: red;
}#numerovidas{
        text-align: center;
        color: red;
        margin-left: 120px;
}
#Comprobar {
  border-radius: 10px;
    padding-bottom: initial;
    color: #FFFFFF;
    background-color: #9933FF;
    width: 100px;
    height: 50px;
    margin: 30px 0px;
    font-size: 14px;  
    float: right;
    margin-right: 20px;
    margin-top: 20px;
}#Solucion {
  border-radius: 10px;
    padding-bottom: initial;
    color: #FFFFFF;
    background-color: #9933FF;
    width: 100px;
    height: 50px;
    margin: 20px 0px;
    font-size: 14px;  
    float: right;
    margin-right: 20px;
    margin-top: 20px;
}
#cabecera {background: #FFCCFF;
        padding: 10px;
        width: 97%;
        height: 60px;
        border: 3px solid #9933FF;
}
img {width: 60px;
    display: inline-block;
}#tiempo{
        float:left;
        margin-top: -130px;
        font-size:30px;
}#conseguido {
        font-size: 50px;
        display: none;
        color: blue;
        background-color: #33FFFF;
        margin: 100px 250px;
}.caja{
        background-color: #FFFFFF;
        color: blue;
        width: 350px;
        height: 75px;
        margin: 100px 425px;
        font-size: 50px;
        text-align: center;
}
#pie {background: #99FFFF;
    text-align: center;
    width: 114%;
    height: 30px;
    border: 5px solid #9933FF;
    color: #FF0033;
    margin-top: 270px;
}
#tabla1 {margin-top: 10px;
        margin-left: 230px;
        background-color: #FFFFFF;
}
.palabra{
        border: 2px solid blue;
        width: 70px;
        height: 70px;
        text-align: center;
        font-size: 50px;
        color: red;
}
#alfabeto{
        margin-top: 30px;
        display:flex;
        justify-content: center;
        align-items: center;
}#alfabetobis{
        margin-top: 0px;
        display:flex;
        justify-content: center;
        align-items: center;
}#alfabetotris{
        margin-top: 0px;
        display:flex;
        justify-content: center;
        align-items: center;
}#alfabetotetris{
        margin-top: 0px;
        display:flex;
        justify-content: center;
        align-items: center;
}
.letras{
        border: 2px solid red;
        width: 50px;
        height: 50px;
        margin: 0px 0px;
        text-align: center;
        font-size: 35px;
}h2{
        margin-left: 100px;
        color: blue;
}

#abajo {width: 15px;
        border: 4px solid #CC33FF;
}#mensajeok{
        font-size: 60px;
        color: #9933FF;
        background-color: white;
        text-align: center;
        margin: 10px 50px;
        display: none;
}#mensajeno{
        font-size: 60px;
        color: #9933FF;
        background-color:white;
        text-align: center;
        margin: 10px 50px;
        display: none;
}#mensajeseacabo{
        font-size: 60px;
        color: #9933FF;
        background-color:white;
        text-align: center;
        margin: 10px 50px;
        display: none;
}#elnumero{
        font-size: 70px;
        color: red;
        background-color:#33FFFF;
        text-align: center;
        margin: 10px 50px;
        
}

<!--Para que no aparezcan las flechitas en la caja --> 
input[type=number]::-webkit-inner-spin-button, 
input[type=number]::-webkit-outer-spin-button { 
  -webkit-appearance: none; 
  margin: 0; 
}
//Firefox:
input[type="number"] {
-moz-appearance: textfield;
}
input[type="number"]:hover,
input[type="number"]:focus {
-moz-appearance: number-input;
}
input[type=number] {
    -moz-appearance:textfield;
}