View source for MediaWiki:Common.css

/* CSS placed here will be applied to all skins */
/* Hide the toolbar for everyone */
#p-tb {
    display: none;
}

/* Apply rounded corners to all images */
img, .thumbimage, .image img {
    border-radius: 5px !important; /* Adjust the value to control the roundness of the corners */
}

/* Prevent large images from overflowing off the page */
img, .thumbimage, .image img {
    max-width: 100%;
    height: auto;
}

.item-tooltip-content {
  box-shadow: 0 0 10px rgba(0, 0, 0, 0.5);
  line-height: 1.2;
  max-width: 300px;
}