Hello everyone, I had this problem updating the moodle version. I struggled looking for the solution and found something that can help.
I did not find the root of the problem but a momentary solution.
In another Moodle copy the CSS code that moodle needed with the problem and embed it in the body from the option "Add html"
I attach CSS code just as I pasted it into the body
"<style>
div.editor_atto_toolbar {display: block; background: # f2f2f2; min-height: 35px; border: 1px solid # 8f959e; width: 100%; padding: 0 0 9px 0} div.editor_atto_toolbar button {padding: 4px 9px; background: none; border: 0; margin: 0; border-radius: 0; cursor: pointer} div.editor_atto_toolbar button + button {border-left: 1px solid #ccc} div.editor_atto_toolbar button [disabled] {opacity: .45; background : none; cursor: default} .editor_atto_toolbar button: hover {background-image: radial-gradient (ellipse at center, # fff 60%, # dfdfdf 100%); background-color: #ebebeb} .editor_atto_toolbar button: active ,. editor_atto_toolbar button.highlight {background-image: radial-gradient (ellipse at center, # fff 40%, # dfdfdf 100%); background-color: #dfdfdf} div.editor_atto_toolbar button :: - moz-focus-inner {border: 0; padding: 0} div.editor_atto_toolbar button .icon {padding: 0; margin: 2px 0} div.editor_atto_toolbar div.atto_group {display: inline-block; border: 1px solid #ccc; border-bottom: 1px solid # b3b3b3 ; border-radius: 4px; margin: 9px 0 0 9px; background: #fff} .editor_atto _content img {resize: both; overflow: auto} .atto_hasmenu {white-space: nowrap} .atto_menuentry .icon {width: 16px; height: 16px} .atto_menuentry {clear: left} .atto_menuentry h1, .atto_menuentry h2, .atto_menuentry p {margin: 4px} .atto_form textarea.fullwidth, .atto_form input.fullwidth {width: 100%}. atto_form {padding: .5rem} .atto_control {position: absolute; right: -6px; bottom: -6px; display: none; cursor: pointer} .atto_control .icon {background-color: #fff} div.editor_atto_content: focus .atto_control, div.editor_atto_content: hover .atto_control {display: block} .editor_atto_menu.yui3-menu-hidden {display: none } .editor_atto_content img: -moz-broken {-moz-force-broken-image-icon: 1; min-width: 24px; min-height: 24px} .moodle-dialogue-base .editor_atto_menu .moodle-dialogue-content. moodle-dialogue-bd {padding: 0; z-index: 1000} .editor_atto_menu .dropdown-menu> li> a {margin: 3px 14px} .editor_atto_menu .open ul.dropdown-menu {padding-top: 5px; padding- bottom: 5px} .editor_atto_wrap {position: relative} .editor_atto_wrap textarea {direction: ltr} .editor _atto_notification .atto_info, .editor_atto_notification .atto_warning {display: inline-block; background-color: # f2f2f2; padding: .5em; padding-left: 1em; padding-right: 1em; border-bottom-left-radius: 1em; border -bottom-right-radius: 1em} .editor_atto_notification .atto_info {background-color: # f2f2f2} .editor_atto_notification .atto_warning {background-color: gold} .editor_atto_toolbar, .editor_atto_content_wrap, .editor_attoizing + textarea {-box -weeting + textarea-box border-box; box-sizing: border-box} .editor_atto_content.form-control {width: 100%; border-top: 0}
</style> "
That worked for me.
Happy coding.