Not sure what theme you are using (the default and Minimal themes have more rounded and pill shaped tags as the default shape), but something like this should work with some adjustments on your end.
/*------- reading mode tag -------*/
.tag[href="#Google"] {
background: #fff !important;
color: #176bef !important;
border: 2px solid #176bef;
line-height: 2em;
font-weight: 500;
padding-top: 1.5px;
padding-bottom: 3px;
}
/*------- source+live preview tag -------*/
.cm-tag-Google {
background: #fff;
color: #176bef;
border-top: 2px solid;
border-bottom: 2px solid;
line-height: 2em;
font-weight: 500;
}
.cm-hashtag-begin.cm-tag-Google {
border-left: 2px solid;
padding-top: 1px;
padding-right: 1px;
padding-bottom: 3.5px;
}
.cm-hashtag-end.cm-tag-Google {
border-right: 2px solid;
padding-top: 1px;
padding-bottom: 3.5px;
}
