////////////////////////////////////////////////// TANK DIV
<h2 class="main-title">Tanks</h2>

<div class="tank-group" id="group-delta">
    <div class="group-header">
        <span class="group-title">DELTA</span>
        <div class="group-chevron">
            <svg width="20" height="20" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2.5"
                stroke-linecap="round" stroke-linejoin="round">
                <polyline points="6 9 12 15 18 9"></polyline>
            </svg>
        </div>
    </div>
    <div class="group-content">
        <?php renderTankBlock(1, true, true); ?>
        <?php renderTankBlock(5, true, true); ?>
    </div>
</div>
<script>
    // 1. Core Logic: Toggle Groups
    function initGroups() {
        document.querySelectorAll('.tank-group').forEach(group => {
            const header = group.querySelector('.group-header');
            const groupId = group.id;
            const state = localStorage.getItem(groupId);

            if (state === null || state === 'true') {
                group.classList.add('collapsed');
            }

            header.addEventListener('click', () => {
                group.classList.toggle('collapsed');
                const isCollapsed = group.classList.contains('collapsed');
                localStorage.setItem(groupId, isCollapsed ? 'true' : 'false');
            });
        });
    }
</script>
//////////////////////////////////////// CONTAINER:
<div class="app-content-wrapper">

</div>