*, *::before, *::after {
    box-sizing: border-box;
}

:root {
    /* Palette Material You - Tema Chiaro */
    --background-color: #F8F9FA; /* Sfondo molto chiaro */
    --surface-color: #FFFFFF; /* Superfici chiare, come la card */
    --on-surface-color: #1F2A38; /* Testo scuro */
    --on-surface-variant: #6C7A89; /* Testo secondario/etichette */
    --outline-color: #E2E8F0; /* Bordo sottile */
    --primary-color: #2D6BFF; /* Blu principale */
    --on-primary-color: #FFFFFF; /* Testo sul blu */
    --shadow-color: rgba(0, 0, 0, 0.08); /* Ombra leggera */
    --focus-color: #2D6BFF; /* Bordo focus blu */
}

:root.dark {
    /* Palette Material You - Tema Scuro */
    --background-color: #121212; /* Sfondo scuro */
    --surface-color: #1E1E1E; /* Superfici leggermente più chiare dello sfondo */
    --on-surface-color: #E0E0E0; /* Testo chiaro */
    --on-surface-variant: #9E9E9E; /* Testo secondario chiaro */
    --outline-color: #3C3C3C; /* Bordo scuro */
    --primary-color: #6EA8FF; /* Blu acceso per il tema scuro */
    --on-primary-color: #121212; /* Testo scuro sul blu acceso */
    --shadow-color: rgba(0, 0, 0, 0.5); /* Ombra più marcata */
    --focus-color: #6EA8FF; /* Bordo focus blu acceso */
}

body {
    font-family: 'Roboto Flex', sans-serif;
    background-color: var(--background-color);
    color: var(--on-surface-color);
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    margin: 0;
    transition: background-color 0.3s, color 0.3s;
}

.converter-container {
    width: 100%;
    max-width: 26rem; 
    padding: 0 1rem;
    margin-left: auto;
    margin-right: auto;
    display: flex;
    justify-content: center;
    align-items: center;
    flex-grow: 1;
}

.converter-card {
    background-color: var(--surface-color);
    padding: 2rem;
    border-radius: 1.5rem;
    box-shadow: 0 0.5rem 1rem var(--shadow-color);
    text-align: center;
    max-width: 22rem; 
    width: 100%;
    margin: auto;
    transition: box-shadow 0.3s, background-color 0.3s;
}

h2 {
    margin-bottom: 2rem;
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--on-surface-color);
}

.input-group {
    margin-bottom: 1.5rem;
    position: relative;
}

label {
    position: absolute;
    top: -0.625rem;
    left: 1rem;
    background-color: var(--surface-color);
    padding: 0 0.5rem;
    font-size: 0.8rem;
    color: var(--on-surface-variant);
    transition: background-color 0.3s, color 0.3s;
}

input[type="number"] {
    width: 100%;
    padding: 1rem;
    border: 0.125rem solid var(--outline-color);
    border-radius: 0.75rem;
    font-size: 1rem;
    color: var(--on-surface-color);
    background-color: var(--surface-color);
    transition: border-color 0.3s, background-color 0.3s;
    outline: none;
}

input[type="number"]:focus {
    border-color: var(--focus-color);
}

#convert-button {
    width: 100%;
    padding: 1rem;
    background-color: var(--primary-color);
    color: var(--on-primary-color);
    border: none;
    border-radius: 0.75rem;
    font-size: 1rem;
    font-weight: 500;
    cursor: pointer;
    transition: background-color 0.3s, box-shadow 0.3s;
    box-shadow: 0 0.125rem 0.25rem rgba(0,0,0,0.15);
}

#convert-button:hover {
    background-color: color-mix(in srgb, var(--primary-color) 90%, black);
    box-shadow: 0 0.25rem 0.5rem rgba(0,0,0,0.25);
}

p#message {
    margin-top: 1.5rem;
    color: var(--on-surface-variant);
    font-size: 1rem;
    min-height: 1.25rem;
}

.theme-switcher {
    position: absolute;
    top: 1rem;
    right: 1rem;
}

#theme-toggle {
    background-color: var(--surface-color);
    border: none;
    cursor: pointer;
    color: var(--on-surface-color);
    padding: 0.5rem;
    border-radius: 50%;
    transition: background-color 0.3s, color 0.3s;
    box-shadow: 0 0.125rem 0.25rem rgba(0,0,0,0.1);
}

#theme-toggle:hover {
    background-color: var(--outline-color);
}

#theme-toggle svg {
    width: 1.5rem;
    height: 1.5rem;
}

footer {
    width: 100%;
    text-align: center;
    padding: 1rem 0;
    color: var(--on-surface-variant);
    font-size: 0.875rem;
    position: relative;
    bottom: 0;
}