style.css

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

body {
   background-color:  #151d26;
   text-align: center;
   align-items: center;
   font-family: Arial, Helvetica, sans-serif;
}

.body-container {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
}

.title {
    margin-top: 25px;
    color: #72b0df;
    font-weight: bold;
    font-size: 30px;
}

.select-temperature {
    display: flex;
    margin-top: 70px;
    font-size: 18px;
    text-align: center;
    align-items: center;
    justify-content: space-between;
}

select {
    color: white;
    font-size: 22px;
    border: 3px solid #72b0df;
    background-color: #151D26;
    border-radius: 7px;
    height: 40px;
    width: 150px;
    margin-left: 10px;
    margin-right: 10px;
    transition: all .2s ease-in-out;
}

select:focus {
    outline: none;
    background-color: #202D3B;
}


.text-complete {
    color: white;
    margin-top: 5px;
    font-size: 20px;
}

.input-container {
    margin-top: 20px;
}

.input-value {
    border: none;
    color: white;
    text-align: center;
    font-size: 24px;
    width: 370px;
    outline: none;
    border-bottom: 2px solid #72b0df;
    background-color: #151d26;
    margin: 15px 0px 10px 0px;
    transition: all .3s ease-in-out;
}

.input-value:focus {
    border-bottom: 3px solid #72b0df;
}

.result {
    margin-top: 20px;
    font-size: 24px;
    color: white;
}

.btn {
    border: none;
    margin: 30px;
    background-color: #72b0df;
    border: 2px solid #437CA8;
    color: white;
    width: 330px;
    font-size: 22px;
    border-radius: 10px;
    height: 48px;
    box-shadow: 0px 5px 0px #437CA8;
    transition: all .2s ease-in-out;
}

.btn:active {
    box-shadow: none;
    transform: translateY(5px);
}

@media screen and (max-width: 768px) {
    .body-container {
        position: absolute;
        top: 0%;
        left: 15%;
        transform: translate(-13%, 0%);
        margin-top: 30px;
    }
}