style.css

* {
    margin: 0;
    padding: 0;
}

body, html {
    height: 100%;
}
body {
    display: flex;
    justify-content: center;
    align-items: center;
    background-color: #c9c0ae66;
    flex-direction: column;
}

.form-container {
    display: flex;
    justify-content: space-between;
    flex-direction: column;
    align-items: center;
    padding: 10px 15px;
    border: 1px solid #1875df;
    border-radius: 10px;
    width: 25%;
    background-color: #81a3e9;
}

.form-container form{
    width: 100%;
}

.form-container .form-title {
    align-self: flex-start;
    font-size: 22px;
    color: #000000;
    padding-bottom: 10px;
    border-bottom: 1px solid #1875df;
    display: block;
    width: 100%;
}

.input-group, .form-check, #send-btn {
    margin: 15px 0;
}

#gender-block, #limbs-block {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 15px;
}

#gender-block, #limbs-block {
    padding: 0;
}

#gender-block {
    margin-right: 50px;
}

#limbs-block .block-title {
    margin-right: 5px;
}

#send-btn {
    display: block;
    width: 100%;
    background-color: #3552cfba;
    border-bottom: 1px solid #1875df;
}