1px horizontal lines

[tiagogon]

On my project i have a gallery with no gutter, just like this one: http://codepen.io/desandro/pen/RPKgEN

does anyone knows why sometimes (it dependes on the window size) this lines appear between elements?

[desandro]

The reason pixel rounding errors. It's a tough issue to resolve because they appear inconsistently. Vertical gaps are a bit more tricky as overlaps may not fix them

See possible fix in metafizzy/isotope#916 (comment) or feature request #795

[wjramos]

When you zoom, do they "flicker" (appear and the disappear with zoom level) ?

This is likely due to sub-pixel rendering differences between browsers. The only real way to address this is by having a .5px (or so) overlap so that it simulates rounding up to the nearest whole pixel