myAccordeon {
    display: flex;
    flex-direction: column;
    flex: 1; /* 🔴 clé du problème */
    min-height: 0;
}



myAccItem {
    border-bottom: 2px solid #cfd8dc;
}
myAccHeader {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 8px 16px;
    cursor: pointer;
    font: 14px/1.4 Segoe UI, Arial, sans-serif;
    color: #455a64;
    background: transparent;
    transition: all 0.2s ease;
}

    myAccHeader:hover {
        color: #0d47a1;
    }
myAccItem.open > myAccHeader {
    color: #0d47a1;
    font-weight: 600;
    border-left: 3px solid #1976d2;
    background: rgba(25,118,210,0.05);
}
myAccHeader .chevron {
    width: 10px;
    height: 10px;
    border-right: 2px solid currentColor;
    border-bottom: 2px solid currentColor;
    transform: rotate(-45deg);
    transition: transform 0.2s ease;
}

myAccItem.open myAccHeader .chevron {
    transform: rotate(45deg);
}
myAccPanel {
    overflow: hidden;
    max-height: 0;
    opacity: 0;
    transition: max-height 0.25s ease, opacity 0.2s ease;
    padding: 0 16px;
}

myAccItem.open > myAccPanel {
    max-height: 1000px; /* volontairement large */
    opacity: 1;
    padding: 8px 16px;
}
myAccordeon myAccPanel {
    flex: 1;
    overflow: auto;
    min-height: 0;
}
myaccordeonheader {
    border: 1px solid darkgray;
    display: flex;
    align-items: baseline;
    cursor: pointer;
    background: #F5F5F5;
}

myaccordeonitem.open myaccordeonheader .down {
    display:block;
}
myaccordeonitem myaccordeonheader .down {
    display: none;
}

myaccordeonitem.open myaccordeonheader .right {
    display: none;
}
myaccordeonitem myaccordeonheader .right {
    display: block;
}