style.css

* {
    padding: 0;
    margin: 0;
    box-sizing: border-box;
    font-family: Arial, Helvetica, sans-serif;
}

body {
    background-color: #1F5EAF;
    height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
}

main {
    background-color: #DC4500;
    width: 35%;
    height: 95%;
    border-radius: 40px;
    box-shadow: 0px 0px 5px 2px black;
    display: flex;
    align-items: center;
    flex-direction: column;
}

#titulo {
    width: 100%;
    height: 15%;
    border-bottom: 4px solid black;
    color: white;
    display: flex;
    justify-content: center;
    align-items: center;
}

#form {
    width: 100%;
    display: flex;
    align-items: center;
    flex-direction: column;
}

.campos {
    width: 90%;
    height: 50px;
    margin: 13px 0px;
    border: 2px solid black;
    border-radius: 10px;
    display: flex;
    justify-content: center;
}

legend {
    margin-left: 10px;
    padding: 0px 4px;
    color: white;
}

input {
    background-color: transparent;
    color: white;
    border: none;
    width: 98%;
    height: 100%;
    padding: 5px;
    outline: none;
}

::-webkit-input-placeholder {
    color: white;
    opacity: .5;
}

#divResultado {
    background-color: black;
    width: 90%;
    height: 180px;
    border-radius: 10px;
    font-size: 13px;
    color: #f5814b;
    display: flex;
    justify-content: center;
    align-items: center;
    flex-wrap: wrap;
}

#buttons {
    /*background-color: black;*/
    width: 90%;
    margin-top: 13px;
    display: flex;
    justify-content: center;
    align-items: center;
    flex-direction: column;
}

.btn {
    background-color: transparent;
    margin-bottom: 8px;
    padding: 5px;
    width: 100%;
    height: 40px;
    border: none;
    border-radius: 10px;
    font-weight: bold;
    cursor: pointer;
    display: flex;
    justify-content: center;
    align-items: center;
}

.calcular {
    background-color: black;
    color: white;
}

.calcular:hover {
    background-color: transparent;
    border: 2px solid #1F5EAF;
}

.limpar {
    background-color: transparent;
    border: none;
}

.limpar:hover {
    border: 2px solid white;
}