Can mobile page only hide identity?

Yes, provide a link to your site.

Hello.

The site I am creating is local.

So

Link the address of my other site using the same theme.

https://siyun2012.wordpress.com/

That’s a WordPress.com site – We don’t support WordPress.com here.

Try this:

@media screen and (max-width: 480px) {
    .site-branding {
        left: -999em;
        position: absolute;
    }
}

Thank you very much.
It works well.
Site identity is gone.
However
The header image is gone.

Apparently
There is a problem with my code.

Help me.

It is my CSS code.

/*
Theme Name: twentyseventeen-child
template: twentyseventeen
*/
.page-wrap { padding-bottom: 0; }
.page .page-wrap .content-wrapper, .single .page-wrap .content-wrapper { padding-bottom: 0; }
.content-area .hentry { padding-bottom: 0; }
.entry-footer { margin-top: 0; }
/*
@media screen and (max-width: 1280px) {
.has-header-image .custom-header-media img,
.has-header-video .custom-header-media video,
.has-header-video .custom-header-media iframe,
.has-header-image:not(.twentyseventeen-front-page):not(.home) .custom-header-media img {
height: auto;
left: 0;
max-width: 100%;
min-height: 0;
-o-object-fit: unset;
object-fit: unset;
position: static;
-ms-transform: none;
-moz-transform: none;
-webkit-transform: none;
transform: none;
}
}

@media screen and (max-width: 1024px) {
.has-header-image .custom-header-media img,
.has-header-video .custom-header-media video,
.has-header-video .custom-header-media iframe,
.has-header-image:not(.twentyseventeen-front-page):not(.home) .custom-header-media img {
height: auto;
left: 0;
max-width: 100%;
min-height: 0;
-o-object-fit: unset;
object-fit: unset;
position: static;
-ms-transform: none;
-moz-transform: none;
-webkit-transform: none;
transform: none;
}
}

@media screen and (max-width: 768px) {
.has-header-image .custom-header-media img,
.has-header-video .custom-header-media video,
.has-header-video .custom-header-media iframe,
.has-header-image:not(.twentyseventeen-front-page):not(.home) .custom-header-media img {
height: auto;
left: 0;
max-width: 100%;
min-height: 0;
-o-object-fit: unset;
object-fit: unset;
position: static;
-ms-transform: none;
-moz-transform: none;
-webkit-transform: none;
transform: none;
}
}

@media screen and (max-width: 480px) {
.has-header-image .custom-header-media img,
.has-header-video .custom-header-media video,
.has-header-video .custom-header-media iframe,
.has-header-image:not(.twentyseventeen-front-page):not(.home) .custom-header-media img {
height: auto;
left: 0;
max-width: 100%;
min-height: 0;
-o-object-fit: unset;
object-fit: unset;
position: static;
-ms-transform: none;
-moz-transform: none;
-webkit-transform: none;
transform: none;
}
}
.custom-header-media:before {
background: none;
}
*/
@media screen and (max-width: 480px) {
.site-branding {
left: -999em;
position: absolute;
}
}
@media screen and (max-width: 480px) {
.has-header-image.twentyseventeen-front-page .site-branding,
.has-header-video.twentyseventeen-front-page .site-branding,
.has-header-image.home.blog .site-branding,
.has-header-video.home.blog .site-branding,
.has-header-image.twentyseventeen-front-page .custom-header,
.has-header-video.twentyseventeen-front-page .custom-header,
.has-header-image.home.blog .custom-header,
.has-header-video.home.blog .custom-header { height: auto;
left: 0;right: 0;
top: 0;
max-width: 100%;
min-height: 0;
-o-object-fit: unset;
object-fit: unset;
position: static;
-ms-transform: none;
-moz-transform: none;
-webkit-transform: none;
transform: none;
}

.has-header-image.twentyseventeen-front-page .site-branding,
.has-header-video.twentyseventeen-front-page .site-branding,
.has-header-image.home.blog .site-branding,
.has-header-video.home.blog .site-branding,
.custom-header-media,
.has-header-image .custom-header-media img,
.has-header-video .custom-header-media video,
.has-header-video .custom-header-media iframe {
position: static;
}

.custom-header-media:before {
background: none;
}

body.has-header-image .site-description,
body.has-header-video .site-description, /*{
color: #fff;
opacity: 0;
}*/

.site-branding .wrap {
padding: 0 1em;
}
.has-header-image:not(.twentyseventeen-front-page):not(.home) .custom-header-media {
height: auto;
left: 0;
right: 0;
top: 0;
}

I’m afraid I cannot replicate the problem, please can you emulate your page using a sandbox tool like: cssdesk.com