/* ==========================================================================
   CORE PRINCIPLES GRID
   Centered heading + description, then three equal-height cards (icon
   circle, title, description). Simpler sibling of .du-help-card
   (_how-we-help.css): same radius/shadow/hover/reveal language, without
   the bento grid-span or link-row behaviour this component doesn't need.
   ========================================================================== */

.du-principles {
    background-color: var(--surface);
    padding-top: 100px;
    padding-bottom: 100px;
}

/* ---- Section header ---- */
.du-principles__header {
    max-width: 640px;
    margin: 0 auto var(--space-xl);
    text-align: center;
}

.du-principles__heading {
    margin: 0 0 var(--space-sm);
}

.du-principles__description {
    color: var(--on-surface-variant);
    margin: 0;
}

/* ---- Grid ---- */
.du-principles__grid {
    display: grid;
    grid-template-columns: minmax(0, 1fr);
    gap: var(--space-md);
}

.du-principle-card {
    background-color: var(--surface);
    border: var(--border-width) solid var(--border);
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-level-1);
    padding: var(--space-lg);
    display: flex;
    flex-direction: column;

    opacity: 0;
    transform: translateY(16px);
    transition: opacity var(--transition-slow), transform var(--transition-slow),
                box-shadow var(--transition-normal), border-color var(--transition-normal);
}

.du-principle-card.is-visible {
    opacity: 1;
    transform: translateY(0);
}

.du-principle-card:hover,
.du-principle-card:focus-within {
    border-color: var(--primary-hover);
    box-shadow: var(--shadow-level-2);
    transform: translateY(-3px);
}

.du-principle-card.is-visible:hover,
.du-principle-card.is-visible:focus-within {
    transform: translateY(-3px);
}

@media (prefers-reduced-motion: reduce) {
    .du-principle-card {
        transition: none;
        transform: none;
    }
    .du-principle-card:hover {
        transform: none;
    }
}

.du-principle-card__icon {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    width: 44px;
    height: 44px;
    border-radius: var(--radius-md);
    background-color: var(--surface-container-low);
    color: var(--primary);
    margin-bottom: var(--space-md);
    transition: transform var(--transition-fast), background-color var(--transition-fast);
}

.du-principle-card:hover .du-principle-card__icon,
.du-principle-card:focus-within .du-principle-card__icon {
    transform: translateY(-2px) scale(1.05);
    background-color: var(--surface-container-high);
}

.du-principle-card__title {
    font-size: clamp(1.2rem, 1.6vw, 1.375rem);
    margin: 0 0 var(--space-xs);
}

.du-principle-card__description {
    color: var(--on-surface-variant);
    margin: 0;
}

/* ==========================================================================
   TABLET — 768–1024px: three columns if space allows, otherwise two
   ========================================================================== */
@media (min-width: 768px) and (max-width: 1024px) {
    .du-principles__grid {
        grid-template-columns: repeat(2, minmax(0, 1fr));
    }
}

/* ==========================================================================
   DESKTOP — >= 1025px: three equal columns
   ========================================================================== */
@media (min-width: 1025px) {
    .du-principles__grid {
        grid-template-columns: repeat(3, minmax(0, 1fr));
        align-items: stretch;
    }
}

/* ---- Mobile ---- */
@media (max-width: 767px) {
    .du-principles {
        padding-top: 48px;
        padding-bottom: 48px;
    }

    .du-principles__header {
        margin-bottom: var(--space-lg);
    }

    .du-principle-card {
        padding: var(--space-md);
    }
}