It looks like you haven't done any theme and templating editing yet. There's a few ways to go about fixing this. The easiest is if you are only going to have people access this through your Joomla page. If so, here are some tips from another post on the SMF site (most importantly, the xhtml to html part).
Quote:
THEMING:
Changing the SMF doc_type from xhtml to html will handle many of the basic "super
large font" issues.
The can be done by changing the line near the top of index.template.php in your SMF
Theme directory.
However, some of the Mambo templates and SMF themes do not play well together.
In the Mambo Template, fixed width templates of less than 500 pixels width are
difficult for SMF to "fit in".
You have two main options.
The first is to increase the basic width of the Mambo Template.
-> In MAMBO/templates/TEMPLATE_NAME/index.php, change the width call of the main
table to something larger...
The second option, which may require some tweaking, is the change the Mambo Template
into a variable width template.
-> In MAMBO/templates/TEMPLATE_NAME/index.php, change the width call of the main
table 100%...
In addition to the width issues, there are some overlaps in the CSS entires between
Mambo and SMF.
The CSS files for Mambo and SMF have some duplicate values that may conflict.
A proper design of the bridged site will include personalized templates/themes for
Mambo and SMF that
will avoid this situation. This may take some time (and effort), however. You can
make a "quick and dirty"
merge of the CSS files by doing the following:
Open the MAMBO/templates/TEMPLATE_NAME/css/template_css.css file
Open the SMF/Themes/THEME_NAME/style.css file
Copy all of the SMF Theme file into the Mambo template file.
Remove the Duplicate entries from the newly copied portion.
(In other words, if the CSS entry exists in the Mambo template, delete the entry in
the newly created SMF section)
Now save it, and then remove the same "duplicate" entries in the style.css file in
your SMF theme directory.
However, you will still have duplicate etc. sections so your page won't be XHTML valid. Might not be a big deal for you.
If you want validation, or you want your forum to be accessible both wrapped an unwrapped, you'll want to either follow the directions posted
here, or find a theme from someone else that has already done that.
