zulip/web/styles/message_view_header.css

#message_view_header {
    color: var(--color-text-message-view-header);
    z-index: 2;
    float: left;
    height: var(--header-height);
    width: 100%;
    line-height: var(--header-height);
    display: flex;
    align-items: baseline;
    white-space: nowrap;
    cursor: default;

    .hidden {
        display: none;
    }

    /* TODO: Remove the `.navbar_title` span from the `message_view_header.hbs`
       template. That span predates the use of flexbox, and makes it so that
       elements like the `.narrow_description` have different line-height and
       sizing contexts depending on whether it's a view or a narrow being shown. */

    .message-header-stream-settings-button,
    .navbar_title {
        padding: 0 2px 0 6px;
        overflow: hidden;
        text-overflow: ellipsis;
        color: inherit;
        text-decoration: none;
        /* Create a flex container for the icon and
           stream name. */
        display: flex;
        /* We want to use baseline alignment so that the
           stream name and narrow description sit on
           the same invisible line. */
        align-items: baseline;

        .zulip-icon {
            /* Pull the icon out of baseline alignment,
               and center with stream name. */
            align-self: center;
        }

        .zulip-icon-inbox {
            /* 16px at 16px em, inherited from .navbar_title */
            font-size: 1em;
        }

        .fa-envelope {
            /* The squatter envelope icon appears
               better vertically centered when aligned
               to the baseline of the adjacent DM partners. */
            align-self: baseline;
        }

        @media (height < $short_navbar_cutoff_height) {
            padding: 0 3.5px; /* based on having ~41.66% decrease */
        }

        & i {
            margin: 0 6px 0 5px;
            /* Align all icons to center. */
            align-self: center;
        }

        .fa {
            .fa-envelope {
                /* 14px at 16px em, inherited from .navbar_title */
                font-size: 0.875em;
                margin: 0 5px;
            }
        }
    }

    .message-header-navbar-title {
        font-weight: 600;
        /* 16px at 14px em */
        font-size: 1.1429em;
        /* Allow long navbar titles (e.g., stream names) to collapse. */
        flex: 0 1 auto;
        overflow: hidden;
        text-overflow: ellipsis;
    }

    .narrow_description {
        /* Flexbox's baseline alignment is responsible for
           matching the description's baseline to the title.
           Here, normal just ensures a comfortable, i18n-friendly
           line height for the description. */
        line-height: normal;
        background: none;
        color: inherit;
        font-weight: 400;
        padding-left: 10px;
        overflow: hidden;
        text-overflow: ellipsis;
        /* The very last element in the navbar is the search icon, the second
        last element is the narrow description (even if it is empty when a
        channel contains no description). The flex-grow property ensures this
        element takes up the entirety of the white space, while flex-shrink
        accommodates narrower viewports. Setting flex-basis 0 enables an
        ellipsis to be displayed, as the 0 takes the place of the max-content
        default that would otherwise run titles under the search box. */
        flex: 1 1 0;
        margin: 0;

        .help_link_widget,
        .fa {
            margin: 0;
        }
    }
}