You have a routing problem. If you look, the one you use for the logo5.png image is images/logo5.png, but you are putting the .css at the same level as the images directory. Just remove ../ from the ../css/bootstrap.css path and leave only css/bootstrap.css and that should work.
You are probably using an include('includes/header.php') inside your index.php file and that is why the image path is correct and your css path is incorrect since by including the header.php markup inside the index.php with the include() function you are putting what is in header.phpinside the level of index.php
EDITED
In the case of still having the error, the next probable cause would be the access privileges to the file. I recommend assigning the corresponding permissions (depending on your Operating System) to read in order to rule out the error.
You have a routing problem. If you look, the one you use for the logo5.png image is images/logo5.png, but you are putting the .css at the same level as the images directory. Just remove ../ from the ../css/bootstrap.css path and leave only css/bootstrap.css and that should work.
You are probably using an include('includes/header.php') inside your index.php file and that is why the image path is correct and your css path is incorrect since by including the header.php markup inside the index.php with the include() function you are putting what is in header.phpinside the level of index.php
EDITED In the case of still having the error, the next probable cause would be the access privileges to the file. I recommend assigning the corresponding permissions (depending on your Operating System) to read in order to rule out the error.