main.css

@import url('https://fonts.googleapis.com/css?family=Quicksand:400,500');

main {
    background-color: white;
    margin-bottom: 4.5rem;
    padding: 1.5rem;
}

.inscription{
    margin: auto;
    max-width: 45rem;
}

.plan__intro-title{
    font-family: "Quicksand";
    font-size: 3rem;
    color: tomato;
    text-align: center;
}

.plan__intro-title::first-letter{
    font-size: 4rem;
    text-decoration: underline dotted fuchsia;
    vertical-align: middle;
}

label{
    display: block;
    margin: 2rem 0;
    font-weight: 500;
}

label:not(.terms){
    text-align: right;
    border-bottom: 1px solid lightslategrey;
}

label>span:not(.read-terms){
    float: left;
}

input,
select {
    border: none;
    outline: none;
    background: transparent;
}
input:not([type="checkbox"]),
select {
    font-family: inherit;
    width: 85%;
    font-size: 1rem;
    border-top-right-radius: .8rem;
}

label>span:not(.read-terms),
input:not([type="checkbox"]),
select {
    display: inline-block;
    vertical-align: bottom;
    padding: .5rem;
}

input:not([type="checkbox"]):hover,
label:not(.terms):hover,
select:hover {
    background: #f5f5f5;
    border-top-right-radius: .8rem;
}

input:not([type="checkbox"]):focus,
select:focus {
    background: #e6e6e6;
}

.selection{
    position: relative;
}

select{
    position: relative;
    -moz-appearance: none;
    -webkit-appearance: none;
    appearance: none;
}

.selection::after{
    position: absolute;
    content: "≡";
    color: #5e5e5e;
    top: 0;
    right: 0;
    padding-right: 0.5rem;
    pointer-events: none;
    text-align: center;
    line-height: 2rem;
    font-size: 1.7rem;
}

fieldset{
    border-radius: 1rem;
}

[type="checkbox"]:focus{
    outline: none;
}

[type="checkbox"]{
    margin: 0;
    -webkit-appearance: none;
    -moz-appearance: none;
    appearance: none;
    display: inline-block;
    width: 1.25rem;
    height: 1.25rem;
    background: transparent;
    border: 2px solid black;
    border-radius: 5px;
    vertical-align: bottom;
}

[type="checkbox"]:checked{
    border: none;
}

[type="checkbox"]:checked::after{
    color: black;
    display: block;
    position: relative;
    content: " ";
    left: 5px;
    width: 5px;
    height: 1rem;
    font-size: 3rem;
    border: solid black;
    border-width: 0 5px 5px 0;
    border-radius: 5px;
    transform: rotate(45deg);
}

input:invalid, label:invalid{
    background: #ff624733;
    border: 1px solid tomato;
}

fieldset{
    text-align: center;
}

.main-buttons{
	margin: .5rem 2rem;
	width: 8rem;
	height: 3rem;
	font-size: 1.1rem;
	color: white;
	border-radius: 3px;
	background: linear-gradient(135deg, fuchsia 85%, #5C0DFF 10%);
	border: none;
	cursor: pointer;
}

.main-buttons:hover{
	/* background: linear-gradient(135deg, fuchsia 85%, #5C0DFF 10%); */
	box-shadow: 7px 7px 0 1px black;
	border-right: 2px solid white;
	border-bottom: 2px solid white;
	position: relative;
	top: -2px;
	left: -2px;
}

@media (max-width:768px){
    input:not([type="checkbox"]),
    select {
        width: 100%;
        font-size: 1rem;
        border-top-right-radius: .8rem;
    }

    label>span:not(.read-terms){
        padding-top: .5rem;
    }
    
    input:not([type="checkbox"]),
    select {
        padding: .5rem;
    }

    .selection::after{
        display: none;
    }

}