Twentyfourteen white space

Yes, Twenty Fourteen uses pseudo selectors to achieve what you want.

E.g.:

.site-content {
    position: relative;
}

.site-content:after {
    background: red;
    content: '';
    display: block;
    height: 100%;
    position: absolute;
    right: -378px;
    top: 0;
    width: 398px;
}

hello, I thanks for your help !
Is that a example I can take and adapt ? So it means that I work on site-content, but let #secondary in 100vh ?

The sidebar will never be full height if you apply styles to it, you will need to mock the sidebar using a pseudo element. Since the ‘site-content’ element contains the 100% height, use that. Inspect the Twenty Fourteen demo site to see how it’s been implemented there.

https://wp-themes.com/twentyfourteen/

You’ll have to consider how it works responsively too.

Ok, I go and try to understand …

Hello Andrew, I really do not understand what I can do … I have inspect the demo, but I don’t find the difference with mine …. I am not very experimented in CSS. Thanks

See: https://snag.gy/MdsyS.jpg ?

I have tried that but no change :
.site-content {
position: relative;
}

.site-content:after {
height: 100%;
position: absolute;
}

Try all of the styles I recommended

WONDERFUL ! It works perfectly, I will check the reponsive …

hello Andrew, almost ok, for the responsive; I have yet white space in the bottom of the page, and in the left side, when I reduce window …

Ah maybe ‘site-content’ isn’t the right element then. Try ‘content-area’ instead.

Thanks Andrew … but it is worst …, #secondary column became too large, and white is staying …