moodle/lib/editor/atto/styles.css

div.editor_atto {
    background-color: white;
    border: 1px solid #BBB;
    padding: 4px;
}

.editor_atto + textarea {
    width: 100%;
    padding: 0;
}

div.editor_atto_toolbar {
    display: block;
    background: #F2F2F2;
    min-height: 36px;
    border-top: 1px solid #BBB;
    border-left: 1px solid #BBB;
    border-right: 1px solid #BBB;
}

div.editor_atto_toolbar button {
    margin-top: 5px;
    margin-bottom: 0px;
    padding: 3px;
    background: none;
    border: none;
 }

div.editor_atto_toolbar button[disabled] {
    opacity: .45;
}

div.editor_atto_toolbar button img {
    padding: 1px;
}

div.editor_atto_toolbar button.atto_strike_button,
div.editor_atto_toolbar button.atto_unorderedlist_button,
div.editor_atto_toolbar button.atto_clear_button,
div.editor_atto_toolbar button.atto_indent_button {
    margin-right: 1em;
}
body.dir-rtl div.editor_atto_toolbar button.atto_strike_button,
body.dir-rtl div.editor_atto_toolbar button.atto_unorderedlist_button,
body.dir-rtl div.editor_atto_toolbar button.atto_clear_button,
body.dir-rtl div.editor_atto_toolbar button.atto_indent_button {
    margin-right: 0px;
    margin-left: 1em;
}

.atto_hasmenu .icon {
    width: 32px;
}

.editor_atto img {
    resize: both; overflow: auto;
}
.atto_menuentry {
    clear: left;
}
.atto_menuentry img {
    width: 16px;
    height: 16px;
}

.atto_menu {
    min-width: 12em;
    background: white;
    padding: 1px;
}

.atto_menu a {
    color: black;
}
.atto_menuentry {
    border-bottom: 1px solid #eee;
    padding: 2px;
}

.atto_menuentry h1,
.atto_menuentry h2,
.atto_menuentry p {
    margin: 4px;
}


.atto_form label {
    display: block;
    margin: 5px;
}