Custom font in backend Winter CMS

[WebVPF]

How do I connect my font to the backend?
I chose a font https://fonts.google.com/specimen/Kelly+Slab?subset=cyrillic

<link rel="preconnect" href="https://fonts.googleapis.com">
<link rel="preconnect" href="https://fonts.gstatic.com" crossorigin>
<link href="https://fonts.googleapis.com/css2?family=Kelly+Slab&display=swap" rel="stylesheet">

I tried to connect the font via import in Customize back-end - Custom stylesheet
/backend/system/settings/update/winter/backend/branding#primarytab-backendlangbrandingstyles

@import url('https://fonts.googleapis.com/css2?family=Kelly+Slab&display=swap');

But the import fails validation.

Is there a way to connect my font to the backend?

[LukeTowers]

What specifically is the error that you are seeing?

[WebVPF]

There is no error after pasting the import. The backend is working.
In the CSS editor for the line with @import
info-tooltip:

@import prevents parallel downloads, use instead.

All other styles written in Custom stylesheet are not connected to backend.
Example:

@import url('https://fonts.googleapis.com/css2?family=Kelly+Slab&display=swap');

nav#layout-mainmenu.navbar-mode-inline ul.mainmenu-nav li a .nav-label,
nav#layout-mainmenu.navbar-mode-inline_no_icons ul.mainmenu-nav li a .nav-label {
    font-family: 'Kelly Slab', cursive;
    font-size: 18px;
}

[AIC-BV]

Have you tried this instead of the import url?
The import url doesn't work for me either.

/* cyrillic */
@font-face {
  font-family: 'Kelly Slab';
  font-style: normal;
  font-weight: 400;
  font-display: swap;
  src: url(https://fonts.gstatic.com/s/kellyslab/v11/-W_7XJX0Rz3cxUnJC5t6fkALfq0k.woff2) format('woff2');
  unicode-range: U+0400-045F, U+0490-0491, U+04B0-04B1, U+2116;
}
/* latin-ext */
@font-face {
  font-family: 'Kelly Slab';
  font-style: normal;
  font-weight: 400;
  font-display: swap;
  src: url(https://fonts.gstatic.com/s/kellyslab/v11/-W_7XJX0Rz3cxUnJC5t6fkoLfq0k.woff2) format('woff2');
  unicode-range: U+0100-024F, U+0259, U+1E00-1EFF, U+2020, U+20A0-20AB, U+20AD-20CF, U+2113, U+2C60-2C7F, U+A720-A7FF;
}
/* latin */
@font-face {
  font-family: 'Kelly Slab';
  font-style: normal;
  font-weight: 400;
  font-display: swap;
  src: url(https://fonts.gstatic.com/s/kellyslab/v11/-W_7XJX0Rz3cxUnJC5t6fkQLfg.woff2) format('woff2');
  unicode-range: U+0000-00FF, U+0131, U+0152-0153, U+02BB-02BC, U+02C6, U+02DA, U+02DC, U+2000-206F, U+2074, U+20AC, U+2122, U+2191, U+2193, U+2212, U+2215, U+FEFF, U+FFFD;
}

[WebVPF]

Thanks! It works.

[AIC-BV]

Glad I could help! 😄