SVG as logo

i hope that WordPress will include the svg support soon.
But you can activate the svg mime type by adding this to your child-theme functions.php:

function custom_mtypes( $m ){
    $m['svg'] = 'image/svg+xml';
    $m['svgz'] = 'image/svg+xml';
    return $m;
}
add_filter( 'upload_mimes', 'custom_mtypes' );

or use that wonderful plugin svg support – it also enables previewing in the media library.

svgs do have on default for WordPress a width and height of zero “0”

Therefore, one must then assign a width to the logo. This can be a very large value and must be an absolute unit for some browsers (so % and em etc. does not work). The adjustment of the size of the logo is done via the display property of the surrounding container.

If you don’t use the option in svg support to force replacement of all svg to inline svg try:

#top .logo img {
width: 450px
}

if you have the inline svg :

#top .logo svg {
 width: 450px
}

as inline svg and shrinking header there are ways to implement the svg support too.
may i see your site?