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

html,body{
    display: grid;
    height: 100%;
    place-items: center;
    background: #050505;
}

.center{
    display: flex;
    text-align: center;
    align-items: center;
    justify-content: center;
}

.outer{
    position: relative;
    margin: 0 50px;
    background: #111;
}

.button{
    height: 70px;
    width: 220px;
    border-radius: 50px;
}

.circle{
    height: 200px;
    width: 200px;
    border-radius: 50%;
}
.outer button, .outer span{
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
}

.outer button{
    background: #111;
    color: #f2f2f2;
    outline: none;
    border: none;
    font-size: 20px;
    z-index: 9;
    letter-spacing: 1px;
    text-transform: uppercase;
    cursor: pointer;
}

.button button{
    height: 60px;
    width: 210px;
    border-radius: 50px;
}
.circle button{
    height: 180px;
    width: 180px;
    border-radius: 50%;
}

.outer span{
    height: 100%;
    width: 100%;
    background: inherit;
}

.button span{
    border-radius: 50px;
}

.circle span{
    border-radius: 50%;
}

.outer:hover span:nth-child(1){
    filter: blur(7px);
}
.outer:hover span:nth-child(2){
    filter: blur(14px);
}

.outer:hover {
    background: linear-gradient(#14ffe9,#ffeb3b,#ff00e0);
    animation: rotate 1.5s linear infinite;
}

@keyframes rotate{
    0%{
        filter: hue-rotate(0deg);
    }
    100%{
        filter: hue-rotate(360deg);
    }
}

@media (max-width: 640px) {
    .center{
        flex-wrap: wrap;
        flex-direction: column;
    }

    .outer{
        margin: 50px 0 ; 
    }
}

/* Botão voltar */
.back-btn {
position: fixed;
top: 20px;
left: 20px;
background: #38bdf8;
color: #0f172a;
padding: 10px 16px;
border-radius: 8px;
text-decoration: none;
font-weight: 600;
transition: all 0.3s ease;
box-shadow: 0 5px 15px rgba(56, 189, 248, 0.3);
}

/* Hover */
.back-btn:hover {
background: #0ea5e9;
transform: translateY(-2px);
box-shadow: 0 8px 20px rgba(56, 189, 248, 0.5);
}