Site Title and Sub title problem
If I understand well your question is: You want your page need to be display correctly depending on the type of device pc desktop, laptop, tablet or iphone. In TikiWiki, some themes are not responsive, but the more recent themes have this feature.
This feature can be tested in your browser, such as Firefox, by going to the Tools menu, selecting Developer Tools, and choosing Adaptive View.
En français: menu outils en haut, ensuite outils developpeur et sélectionner Vue adaptative pour testé votre page.
In Tiki, this is managed in the Theme and Appearance menu. Check the box for Fixed Width.
En Français: Dans Tiki, Thème et apparence, mise en page générale et vérifier que la boite de largeur fixe soit activé.
I believe this is managed in the theme. However, it is true that your title is long.
I hope I can help
J'espère que cela peut vous aidez