"Hum" Theme : Text overlaps content field

1 hour later
I found a way to make my content field bigger by adding this code:
#primary {
width: ***px;
}
But the text still overlaps!
Cannot find the way to make it fit.

2 hours later…

Now I found that my problem occurs only with pages, not with posts.
So my questions changes into :
How could make the text of my pages fit to the page size?

Thanks a lot for your advices and for this forum that helps a lot beginners like me, or advanced as well, I guess.

I believe this was caused by an up-stream change in the styles for Twenty Eleven, but I fixed it using this CSS rule in hum’s style.css:

/* Do not force 100% width on one-column sites */
.one-column.singular .entry-header,
.one-column.singular .entry-content,
.one-column.singular footer.entry-meta,
.one-column.singular #comments-title {
        width: auto;
}

Thanks a lot msenate for your good advice. Actually I also found a help in the french WP forum, and the advice was the same as yours, except the first line ( /* Do not force 100% width on one-column sites */ ), which was missing.
So I added it to my child theme Css, but I did not remark any changes, it works the same without it. So is it really necessary?

Hmm, it’s hard for me to say since it’s not clear how the change was tested. I found that CSS rule to work, but that might also be a browser-dependent change. It’s also possible that while testing you did not clear your cache, and therefore it seemed to be fine even if you reverted back to the previous styles. Can you link to the French WP forum note?

Hello msenate,
Actually I pasted your full code and it works fine. Possible that at the time I forgot to empty my browser cache. I don’t remember.
But anyway the issue is resolved now.
Here is the link to the French forum note.
Thanks again for your help.

no problem, cheers!