Template:Panel/styles.css

#collapsible-panel {
    display: flex; 
    flex-direction: column; 
    background: #ffffff; 
    border-radius:5px;  
    box-shadow: 0 2px 3px rgba(85, 85, 85, 0.1), 0 0 0 1px rgba(85, 85, 85, 0.1);
    transition: box-shadow 0.2s ease-in-out;
    width: 100%;
}

#collapsible-panel .mw-collapsible-text {
	display: none;
}

#collapsible-panel:hover,
#collapsible-panel:focus{
    box-shadow: 0 2px 3px rgba(85, 85, 85, 0.25), 0 0 10px rgba(85, 85, 85, 0.25);
}

#collapsible-panel #header {
    font-weight: 600;
}