Text Editing & Layout apparence

With my new website theme, I notice that text spacing is fine in the website back end and it appears differently in the front end. Example, if I add on space between to paragraphe, in the font en that space will look very big (2 -3 times bigger). Even the regular space between line are very big. I would like it to have normal space like here, for example...

Is there a Css code I can add to make the site respect the way I write in the text editor? The site is http://positifstyle.com/guide-incontournable-de-lethique-sur-les-medias-sociaux/

Thank in advance for your help.