I looked through similar questions and found no answer in any of them. Added to the site font. I added the code from the font-kit to the basic css-file, taking into account my structure:
../src/ βββ apps βββ base βββ common β βββ font β β βββ open-sans β β βββ font.ttf β β βββ font.eot β β βββ font.woff β βββ static β β βββ css β β βββ base.css β βββ templates β βββ views options @ font-face that you tried
@font-face { font-family: 'open_sansbold'; src: url('../../font/open-sans/OpenSans-Bold-webfont.eot'); src: url('../../font/open-sans/OpenSans-Bold-webfont.eot?#iefix') format('embedded-opentype'), url('../../font/open-sans/OpenSans-Bold-webfont.woff') format('woff'), url('../../font/open-sans/OpenSans-Bold-webfont.ttf') format('truetype'), url('../../font/open-sans/OpenSans-Bold-webfont.svg#open_sansbold') format('svg'); font-weight: normal; font-style: normal; } @font-face { font-family: 'open_sansbold'; src: url('/common/font/open-sans/OpenSans-Bold-webfont.eot'); src: url('/common/font/open-sans/OpenSans-Bold-webfont.eot?#iefix') format('embedded-opentype'), url('/common/font/open-sans/OpenSans-Bold-webfont.woff') format('woff'), url('/common/font/open-sans/OpenSans-Bold-webfont.ttf') format('truetype'), url('/common/font/open-sans/OpenSans-Bold-webfont.svg#open_sansbold') format('svg'); font-weight: normal; font-style: normal; } But the font does not apply to the element:
.element__symbol { position: absolute; left: 10px; font: bold 15pt open_sansbold; } When inspecting the page, it gives open_sansbold, but a serif font is used. 
UDP Added the structure of the project, it shows where the fonts and the base style file are located.
../../this is below the root list, there is no access there unless of course you are above the two folders above. Better to just insert from the root/font/open-sans/OpenSans-Bold-webfont.eot')- Artem Gorlachev