style.css

body {
    margin: 0;
    padding: 0;
    min-height: 100vh;
}

h1, h2, h3, h4 {
    margin: 0;
    padding: 10px 0;
}

h1 {
    text-align: center;
    margin: 0;
    padding: 20px 0;
    background: #efefef;
}

h3 {
    min-height: 22px;
}

.content {
    min-height: 100vh;
    margin: 0 auto;
}

section {
    padding: 15px 30px;
}

section h2 span {
    font-weight: 100;
}

section#depenses {
    background: rgb(255, 239, 239);
}
section#recettes {
    background: rgb(239, 255, 240);
}
section#epargne {
    background: rgb(246, 239, 255);
}

.row {
    display: flex;
    flex-direction: row;
}

.row > .column {
    flex: 1;
}

.row > .column-2 {
    flex: 2;
}

.row > .column-3 {
    flex: 3;
}

.field {
    margin-bottom: 10px;
}

.field label {
    display: block;
}

.field label::first-letter {
    text-transform: capitalize;
}

.required-star {
    color: red;
}

input {
    text-align: right;
    font-size: 16px;
    max-width: 100px;
}

#message {
    font-size: 16px;
    padding: 30px;
}

#message.positive {
    color: green;
}

#message.neutral {
    color: orange;
}

#message.negative {
    color: red;
}