/* ==================================== */
/* 🎨 VARIABLES & STYLES DE BASE */
/* ==================================== */
:root {
    --black: #000;
    --white: #fff;
    --grey: #333;
    --background-light: #fafafa;
    --shadow-color: rgba(0,0,0,0.1);
    --header-height: 70px; 
}

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

html {
    scroll-behavior: smooth;
    scroll-padding-top: var(--header-height);
}

body {
    font-family: 'Inter', sans-serif;
    background: var(--white);
    color: var(--black);
    /* Correctif vide blanc mobile */
    overflow-x: hidden;
    width: 100%;
}

a {
    text-decoration: none;
    color: inherit;
}

/* ==================================== */
/* ⬆️ BOUTON RETOUR HAUT (Global) */
/* ==================================== */
.back-to-top-button {
    position: fixed;
    bottom: 30px;
    right: 30px;
    z-index: 50;
    background-color: var(--black);
    color: var(--white);
    border-radius: 50%;
    width: 50px;
    height: 50px;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.5rem;
    font-weight: 600;
    box-shadow: 0 4px 10px var(--shadow-color);
    opacity: 0;
    transform: translateY(20px);
    transition: opacity 0.3s ease, transform 0.3s ease;
    visibility: hidden;
}

.back-to-top-button.visible {
    opacity: 1;
    transform: translateY(0);
    visibility: visible;
}

.back-to-top-button:hover {
    background-color: var(--grey);
}