As you all know you can define the allowed fonts that can be used in the editor but you can not easily set the default font.
It defaults to the typical "Times Roman" font.
To set the default font to match your website default font-family do the following;
Search for the code that looks similar to this.
Note: It will not be the same as this example as every ktml instance can be different, depending on your ktml configuration.
<script type="text/javascript"> art_content_config = { "width": 700, "height": 450, "show_toolbar": "load", "show_pi": true, "background_color": "#FFFFFF", "strip_server_location": true, "auto_focus": false, "module_props": { }, "buttons": [ [1, "standard", ["cut", "copy", "paste", "undo", "redo", "find_replace", "toggle_visible", "spellcheck", "toggle_editmode", "toggle_fullscreen", "help"]], [1, "formatting", ["bold", "italic", "underline", "align_left", "align_center", "align_right", "align_justify", "numbered_list", "bulleted_list", "outdent", "indent", "clean_menu", "foreground_color", "background_color", "superscript", "subscript"]], [2, "styles", ["heading_list", "style_list", "fontsize_list"]], [2, "insert", ["insert_link", "insert_anchor", "insert_table", "insert_image", "insert_file", "insert_template", "horizontal_rule", "insert_character"]] ]
Now add these two line just below the "background_color": "#FFFFFF", entry
"font_family": "Arial, Geneva, Helvetica, sans-serif", "font_size": "12px",